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Biographical Memoirs: Volume 57 (1987)

Chapter: Bessel Kok

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Suggested Citation:"Bessel Kok." National Academy of Sciences. 1987. Biographical Memoirs: Volume 57. Washington, DC: The National Academies Press. doi: 10.17226/1000.
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BESSEL KOK November 7, ~91~—April 27, ~979 BY J. MYERS TH E D E C A D E ~ 955-l 965 was a period of revolution in our thinking about the process of photosynthesis. A key event was the realization that the process, long assumed to require only one photoreaction, actually required two. A key figure in the revolution was Bessel Kok. In the following years Bessel and his collaborators in work that bore the stamp of greatness Flee in much of the framework for the Z-scheme mocle! of the energetics of pho- tosynthesis. A preclictable result was the recognition that fol- lowecI. There was a Kettering Research Award in 1963 given by the Charles F. Kettering Foundation ancI the National Academy of Sciences. There were two awards from the American Society of Plant Physiologists: the Charles F. Ket- tering Awarct in 1972 and the Stephen Hales Awarcl in 1978. Anc! there was election to the National Academy of Sciences in 1974. In composing this memoir for Bessel Kok ~ shall use freely the thoughts of collaborators, family, and friends, which are recognizes] only partially in the acknowlecigment at the end. ~ was for almost thirty years a distant colleague, a sometime confidant, a scientific admirer, anct a friend all of which accounts for the highly personal tone of this ac- 125

126 BIOGRAPHICAL MEMOIRS count. But it wouIcl be difficult for anyone to write otherwise because Bessel was a very personal person. Bessel Kok was born November 7, HIS, in the village of Hardinxveld, The Netherlands. His father, Tohannes Evert Kok, was the principal of a local school; he is remembered as a talented man who cast himself in the image of a professor, a puritan Calvinist who lived at the hand of the Bible. His mother, Cornelia Gronclys-Kok, is remembered as "the image of Bessel in female form." Bessel was the oiliest in a family of six chilctren. He remembered his chilc~hood as happy, al- though it was interspersed with the many frustrations that must have arisen for an inventive and energetic boy encum- berecl by a conservative father. Bessel's own statement about his education was that he "never stuctiect" and that he coasted through his high school and college years. Nevertheless, he assimilated a broad back- ground in science anct cleveloped the self-ctiscipline he neeclec! thereafter. His college years began at the University of Leiclen in 1934; they led to the unclergraduate degree of Candidate of Natural Philosophy in 1938 and the advanced degree of Doctor of Natural Philosophy in 1941. An even more significant event occurred! in 1938 when Bessel met Cornelia Hendrika Vogelesang at a Christian Stuclent's Club. Cornelia or Nell, as she became known to all hac! been born and raised in TancIjung Pinang, Indonesia. Her mem- ory of meeting Bessel is one of instantly recognizing him as her future husband. In 1941 Bessel began work toward a Ph.D. in biophysics at the University of Utrecht. In that era the road towarc! a degree was tortuous and at times must have seemed impos- sible. Following the German occupation in 1940, young men were conscripted for labor camps in Germany. But for all it was a time of struggling merely to survive. To provide some protection against conscription, Nell and Bessel were mar-

BESSEL KOK 127 ried in 1943. And although she was selclom successful, Nell clid her best to hicle Bessel. He, on the other hanct, was more inclined to trust to his luck anct the weak support of a pass- port with a falsely increased statement of age. Bessel had become assistant manager of a distilling company, Johan Kos- ter. He also improvised a small ctistillery at home to produce gin from rye and beets; the gin was readily bartered for food. Their first chilcI, Lily, was born in March of 1945, two months before the end of the war. Nell remembers it as the "worst time" for an impoverished and starving people. With the ens! of the German occupation, Bessel was free to turn his efforts from survival to science. The firm of Than Koster provided him both with employment and some direct support of the research for his dissertation, which was pre- sented early in 1948. In the foreword of the dissertation, Bessel recognizes with thanks his professors Bungenberg do Jong and Baas Becking at Leiden. Professor Koningsberger is namect as the Hooggeachte Promotor, but it is also maple clear that E. C. Wassink was the real supervisor. Hence, Bessel's "scientific genealogy" traces to the Biophysical Research Group uncler the direction of A. I. Kluyver and J. M. W. Milatz. Bessel's dissertation was a study of the quantum yield of photosynthesis in the alga Chlorella. It is not now, and was not then, a very exciting document. One clifficulty was that the subject itself, which had been hot in the early 1940s, was only smoldering in 1948. A second difficulty was that a quantum yield, usually expressed as the reciprocal or quantum num- ber (quanta absorbed per oxygen molecules evolved), is ac- tually no more than a number. Its validity hinges only on the nitty-gritty details of measurement. It must be a source of amazement to much of the scientific worict that the quantum yield! of photosynthesis should have engendered so many man-hours of work and yet so much

128 BIOGRAPHICAL MEMOIRS controversy. Certainly one of the many aspects of an expla- nation of this circumstance is historical. In 1923 Otto War- burg tract reported a minimum quantum number of 4.3, nat- urally interpreted as 4. In its time this was an heroic accomplishment. Warburg had invented a manometric method for the measurement of gas exchange. Anct he tract introduced a convenient plant material, the alga Chiorella. There were several acictitional features of experimental pro- toco! that turned out to be important. The first was the use of optically clense cell suspensions that absorber! virtually all the light. Hence quanta absorbed from a monochromatic light beam couIcl be counted simply as incident quanta. The second feature was an assumption that oxygen evolution of photosynthesis was properly evaluated from pressure changes observed in short light periods minus those observed in alternating short dark periods. Considering the theoretical significance of the quantum number, it is remarkable that Warburg's value went unchal- lenged for some fifteen years. By the early 1940s, however, other measurements hac! been made. The number 4 was in doubt as being too low, and the special experimental protocol was being questionecl. Bessel's choice of experimental conditions shows his in- sight anct understanding of the problem. First, he maintained conditions of steady-state photosynthesis and measured ox- ygen evolution over a long time period (an hour). Seconcl, to ensure steacly-state conditions in all cells, he used optically thin suspensions. (Otherwise, cells in a shaken suspension wouIcl alternate between periods of light and virtual dark- ness.) This required mastery of the technology of the Ul- bricht sphere, a device for measuring fractional absorption by a light-scattering cell suspension. A third important choice was that for each cell preparation he measured rates of ox- ygen evolution at several different light intensities. Then the

BESSEL KOK 129 slope of the expected linear plot of oxygen per second versus absorbed quanta per second would give the quantum yield. The quantum numbers obtained from forty-two sets of mea- surements fell within the range 6.5 to 10.0. Bessel deduced that 7.5 was "the most favorable value." In addition to fincting that the quantum number was high (7 to 10) rather than low (4 to 5), Bessel discovered a related phenomenon. The curve for the oxygen rate versus the quantum rate hac! two linear segments with slopes in the ap- proximate ratio of Al and converging near the compensa- tion point where photosynthesis just balances respiration. The phenomenon, which has come to be called the Kok ef- fect, is commonly thought of as resulting from a "suppression of respiration." It provides a possible explanation for low quantum numbers (as 4 to 5) observer! at very low light in- tensities below the compensation point. In 1949, Bessel joined the Solar Energy Research Group of the Organization for AppliecT Scientific Research (T.N.O.) under E. C. Wassink at the Agricultural University in Wag- eningen. This was an excellent match for his needs. As he later wrote on an employment record, it provicled for "full time research, freedom, adequate services." A major mission was the mass culture of algae, a subject that Bessel followed, albeit sporadically, for the rest of his life. An immediate ques- tion was the maximum efficiency of Chlorella in producing total cell material, the efficiency for growth. Bessel's result was an efficiency of about 20 percent (equivalent to a quan- tum number of about 10), which still stancis as a benchmark. Simply growing algae, however, was too bland for Bessel's taste. Most of his efforts went into attendant basic problems. There is an ultimate limitation on the yielcl of algae that can be achieved under sunlight illumination. The problem is that photosynthesis and growth become rate limitect at a light intensity far less than that of midday sunlight. Those of us

30 BIOGRAPHICAL MEMOIRS concerned with mass culture naturally sought ways to circum- vent the limitation. Of several possibilities the most interest- ing was to take advantage of the intermittent light effect of photosynthesis. With sufficient turbulence in a dense culture, individual algal cells move rapidly into and out of the illu- minated front surface and thereby receive high light only in flashes. It was well known that short flashes could be used with higher efficiency, but the time parameters of the effect were not known. Bessel set out to study photosynthesis in flashing light. Bessel spent much of 1951-1952 on leave from Wagen- ingen and as a fellow of the Carnegie Institution in the De- partment of Plant Biology at Stanford under Stacy French. The family now with two chilctren, Lily and young Besse}- livect in the oic! barracks-like buildings that later became the Stanford Research Institute. ~ first met them there and was attracted by the happy self-sufficiency of a family learning the ways of a strange land. Bessel's part of the laboratory became a shambles of equipment-building, and he was frus- tratecT by the slow progress of a machinist who was construct- ing a sector for light chopping. His work at Stanford was reported in a chapter of the 1953 Carnegie monograph on algal culture, and it provider! at least a partial answer: any reasonable turbulence conic! be expected to give some gains in the yield of an algal culture under sunlight. Large gains, requiring very short flashes, probably would be impractical because of the power cost for the necessary turbulence. On his return from Stanford, Bessel began extending his work with flashing light to an attack on the kinetics surround- ing the photochemical events in photosynthesis. His remark- able experimental talents now came into play. He used a high- intensity projection beam that could be chopped and/or attenuated there were two coaxial sectors that allowed in- (lependent variation of both the light and the clerk periocls. .

BESSEL KOK 13 AS a side effort, he hac! cleveloped almost to ultimate lim- its—the measurement of gas exchange by volumetry. Now he couIct choose a very small reaction vessel (<5 mm diameter coupled to a volumeter arrangement that measured oxygen evolution with high sensitivity. The broacl scope of the ex- periments proviclect an unequivocal answer to a twenty-year controversy about the reality of the "photosynthetic unit." The oxygen yield from short flashes confirmed the earlier fincting of R. Emerson and W. A. ArnoIcI: a maximum flash yielct inclependent of temperature and equivalent to about one O2 per 2,000 chlorophylls. Lengthening the flashes gave a temperature-dependent flash yield approaching the rate observed in continuous saturating light. Bessel again went beyond the immediate anc! obvious objective in order to ob- tain an explanation of earlier and apparently conflicting re- sults. In 1955 Bessel again visitec! the United States for two meetings: a Gatlinburg conference on photosynthesis fol- lowocl by a woric! symposium on applied solar energy at Tuc- son and Phoenix. E. C. Wassink also was in attendance. It was evident to all, however, that Bessel tract attained the status of an inclepenclent and innovative scientist. The sectors of Bessel's flashing light apparatus must never have coolecl (town for very long. Within a year after the mea- surement of oxygen flash yielcis, the apparatus was recle- signecI. Now the reaction vessel was a cuvette that was cross- illuminated by a weak measuring beam from a monochro- mator. Any small changes in the transmission of an algal or chioroplast suspension couIcl be observed by a photocell. Were there absorption changes that might reveal photochem- ical intermediates formed cluring a short flash and removed cluring the following ciark period? There were. Actually there were several absorption changes observable across the spectrum. Bessel zeroed in on one of these, a reversible ab-

132 BIOGRAPHICAL MEMOIRS sorption change at 700 nm that he speculated might be the "eventual final photoreceptor of photosynthesis." At this point the tribute of Lou Duysens is appropriate: "The long working hours and inexhaustible inventivity and drive nec- essary to get such an apparatus working successfully in a rel- atively short time, anct to carry out ant] analyze a large num- ber of experiments, were amply rewarcled....Besse} ctiscoverect the far-red absorption changes associated with the reaction center P700 of system IN By 1957 Bessel's accomplishments had become highly vis- ible. He had outgrown his position at Wageningen, and no appropriate position in The NetherIancls was open. Like many Dutch scientists before him, Bessel tract become avail- able for export. A position as clirector of a new institute in West Germany was offered; Bessel ancT Nell visited and to- gether concluded that they shouIcT reject the offer. One major consideration was that the rigidity and formal protocol of the establishment was incompatible with their own life-style. Among other inquiries was one from the Research Institute for Acivancect Studies (RIAS) in Baltimore. By 1958 the Kok family now with three children—hacI found a new home in northwest Baltimore, not far from the converted mansion that housed the RIMS laboratories. RIAS was then about two years oIc} and not well known even in the United States. It was a subsidiary of the Martin Company, a corporate investment as an institute for basic science. In the course of a European trip, its director, Wel- come Bencler, tract stopped to see Bessel in Wageningen, anc! his recruitment was that simple. Bessel electecT to accept a position as a "staff scientist" in an unproven, industrially sup- ported institute. There were no trappings to the position- ' L. N. M. Duysens, "In Memory of Bessel Kok," in Proceedings, Fifth International Congress on Photosynthesis, ed. G. Akoyunoglou (Philadelphia: Balaban International Science Services, 1981), pp. xix-xx.

BESSEL KOK 133 not even the conventional one of academic rank but only the promise of logistic support and freedom of choice in re- search. Bessel tract joined a small group labelled "Bioscience" and with a common bond of interest in photosynthesis. Within the year he tract become the cle facto leacler of the group. No one worked harder, sprouted ideas faster, or drank more martinis at Friday afternoon parties. Welcome Bender man- aged the whole institute with the light touch of one who understood the neecis of basic research. T was one of many visitors who joined in the excitement of the place. In later years other corporate managers were less supportive, but by that time Bessel and his group had achieved a position of strength. In a former wine cellar Bessel assembled an improved version of his machine, which now couIc! be called a split- beam phosphoroscope. A new sector program allowect mea- surements just before anc! just after the flash and was espe- cially useful in studying the absorbance changes near 700 nm. Now the characteristics of the "700 pigment" were re- ve-aled: it was repeatedly bleachect, even by rather weak flashes of far-rect light, and its absorption regained in each subsequent dark period. Of course the measuring light (as at 700 nm) was itself a "far-red." If the measuring beam was macle brighter, there was nothing left for far-red flashes to bleach. But now a new behavior appeared: if the flashes were rec! (insteact of far-red), then each flash restored absorption of the "700 pigment." Here were reciprocal effects of recI and far-red light like those clescribec! by Robert Emerson for the quantum yield of oxygen evolution. At this stage Bessel acquired a young collaborator: George Hoch, a biochemist. The collaboration doubled the number of techniques of measurement but far more than cloublect the imaginative interaction of two minds bouncing ideas back

134 BIOGRAPHICAL MEMOIRS anct forth. The first fruit of their effort came in a joint paper in a 1960 symposium entitled "Light anct I,ife." In that paper they opened the modern era of thinking about photosyn- thesis by the first explicit statement that there must be two photochemical reactions "the first sensitizer! by chlorophyll a and a direct photochemical bleaching of P700; the second sensitize<] by accessory pigment, acting indirectly via media- tion of dark steps, and restoring P700." The hypothesis was rephrased in other ways, presented as a diagram, and con- siderect in terms of other relatecl phenomena. Bessel ancI George had come with the ultimate excitement of science: they hac! discoverecl and unclerstooct an important truth that no one else hacl yet seen. But the reception of their paper was a disappointment. From the record of discussion one wouicl judge that they had cIropped an egg instead of a bomb. They hac! made the tactical error of presenting too many tiara, too many kincis of experiments. Most of the questions centered on experimental details that now appear trivial. Unfortunately, publication of the symposium proceedings was delayed for over a year. By that time important publica- tions from the laboratories of Lou Duysens anct Robin Hill had derivecl indepenclently the two-light-reaction hypothesis from other (lata. And the Hill-Benclall mocle! became the convenient Z-scheme. By 1960 the "black box" of photosynthesis had been opened up, and its bits and pieces were strewn about. The following clecacle was a time of fitting the pieces together. Now Bessel's work moved into high gear. It was remarkable in terms of the number of papers published and the variety of subjects adciressed. It was even more remarkable in the number and diversity of collaborators: some came as senior scientists, some as postdoctoral stuclents, and some as tech- nicians; some even came from the ranks of high school stu- dents employee! by the lab each summer. In the midst of this

BESSEL KOK 135 rather frantic pace, two particular events should be recordecl. In 1963 Bessel and Andre Jagendorf served as coorganizers for a photosynthesis conference helc! at Airlie House in Vir- ginia. In spite of the burden of new information let loose by the two-light-reaction hypothesis, that meeting is remem- bered as a very light-heartect conference.2 And in 1964 Nell and Bessel became citizens of the United States. Another event that became memorable was the extenclecl visit of Anne ant! Pierre Joliot in 1967. This was something more than collaboration; rather, it was a convergence of the conceptual and instrumental developments of two laborato- ries. The Joliots had clevelopec! the art and technology of the polarographic measurement of oxygen at a platinum elec- trocle. They brought this too! with them and sharpened it still further to measure reduction of a low-potential viologen dye by the reducing side of the photosynthetic mechanism. Together with techniques already available, there were now multiple windows through which to view interaction between the two photoreactions. The resultingjoint papers were mag- nificent in the simplicity and clarity they brought to a com- plex subject. On his return to France, Pierre Joliot engaged the acti- vation phenomenon for oxygen evolution that he had clis- coverec} years before. After several minutes of darkness there was a clelay in oxygen evolution cluring the first seconds of light. Now he observed the oxygen yields from short elec- ~n sequence after a clerk periocl. Flash yields (Y) showed an interesting oscillation with a period of four: Ye was zero, Y2 was small, and Y3 was maximum ancT almost twice the steacly-state yield to which the system clamped out after several cycles. The pattern of oscillation tronic flashes given 2 A. Jagendorf, '`In Memory of Bessel Kok," in Proceedings, Fifth International Con- gress on Photosynthesis, ed. G. Akoyunoglou (Philadelphia: Balaban International Sci- ence Services, 1981), pp. xxi-xxiii.

136 BIOGRAPHICAL MEMOIRS obviously contained information about the cryptic events of oxygen evolution. Pierre was led to a clouble two-step mocle} that released two oxygen atoms in sequence. Bessel, now working in(lepenclently, repeated the measurements anct ob- servec! the oscillations, though with some small differences: Y2 was very small and Y3 was often much more than twice the steady-state yielct. Though small, the differences were real, and they were incompatible with Pierre's model. They lee] Bessel to a flurry of effort that taxed the stamina of his younger colleagues. He assembled their elegant experiments to create a simple linear mode! that accumulated I-2-3-4 charges to produce a molecule of oxygen. With a character- istic touch, Bessel called his mode} the "oxygen clock." In retrospect it appears that rather small technical improve- ments lecl Bessel to a mocle} that was simpler and apparently more nearly correct than that which Pierre hacI clerivecI. The history of research on photosynthesis records some acrimo- nious debates and personal animosities that arose uncler less stressful conditions. It is a tribute to both men that, in spite of the clash of their scientific results, they continucct to be close personal friends, communicated their current findings to each other, and became joint authors of a review paper. Following the oxygen clock there were obvious problems of proton release that like oxygen -couict be cligitized by flash illumination. Anc! quietly pursued in the background was continuing development of mass spectrometric measure- ments applied first to the interactions between photosyn- thesis and respiration and later to an extraterrestrial life cle- tection system. It would take a rather detailed catalog- which in fact is provided by the bibliography to do justice to the work of Bessel and his many collaborators. Bessel Kok died in Baltimore on April 27, 1979, after a prolongect battle against lymphoma. He is survives! by his wife, Cornelia Hendrika Nell a quietly resourceful lady

BESSEL KOK 137 who once hid him from labor camp conscription, later helped him reach out for his ambitions, and shared his love of family. She lives in the home into which the Koks first moved in 1958. Also surviving is a daughter, now Cornelie Angeline Forbush; two sons, ~ohannes AlIart Bessel and Allart Alex- ander Bessel; and three grandchildren. Among Bessel's scientific family of colleagues and friends there are many memories. From that legacy, at least a few recollections that provide special insight should be set down . . . In writing: . He appreciated a good hypothesis deeply and had the strength of character not to let an ugly fact stand in the way. · He had a knack for discerning the "nuggets" of a prob- lem. · He was extraordinarily open-minded to any new con- cept or experiment, even if it came from a younger or un- known scientist and even if it was a contradiction to his own ideas. · He could make you a better scientist just by asking ques- tions. · He had a basic belief that if he could measure anything with ten times greater sensitivity than had been achieved be- fore, he was bound to discover something new. · He had learned to smile while criticizing. · He was always searching, either for a simpler hypothesis or for a better joke. An appropriate conclusion to this memoir is taken from one of the several tributes3 to Bessel that have been written. 3 G. Cheniae and J. Myers, "Bessel Kok (1918-1979): A Tribute," in Photosynthesis I: Energy Conversion in Plants and Bacteria, ed. Govindjee (New York: Academic Press, 1982), pp. xxi-xxiii. Reprinted by permission. See footnotes 1 and 2 for two other tributes. A fourth is L. N. M. Duysens and C. J. P. Spruit, "In Memoriam Bessel Kok (1918-1979)," Vakbl. Biol., 59 (1979):210.

138 BIOGRAPHICAL MEMOIRS Bessel's scientific accomplishments reveal too little of a unique char- acter that had many facets. Some may have seen only the outer veneer as a brusque and, at times, even boorish personality. Some may have felt his patience and his sensitivity to all people, whatever their walk in life. Some may have seen his intolerance of the trappings or of the pomp and cere- mony of science. Some have enjoyed him as a witty and boisterous drinking companion. Bessel was an uncommonly dedicated man, dedicated to his family, to his science, and to the joys of life. He pursued each endeavor with unre- lenting fervor and passion and with enormous mental and physical stam- ina. He wore only a thin cloak of inhibitions, happily shared warmth and encouragement, but also gave sharp and sometimes brutal criticisms. His standards for his own work were uncompromisingly high, and he expected as much from others. Many of us earned his criticisms, some experienced his praise and encouragement, but all of us learned from Bessel. On behalf of . . . many we salute and toast you, Bessel, for your scien- tific accomplishments, for your free spirit, and for all the fond personal remembrances you gave us. ~ A M ~ N D E B T E D to Nell Kok who shared with me the story of her life with Bessel. I am indebted to Richard Radmer who assembled the bibliography and provided data from files of the Martin Mari- etta Laboratory. And I am grateful to many others of the Kok circle who shared their thoughts and recollections, notably, Welcome Bender, Leonard Bongers, George Cheniae, Lou Duysens, George Hoch, Andre Jagendorf, Anne and Pierre Toliot, Olga Owens, and Pete Zill.

BESSEL KOK BIBLIOGRAPHY 139 1940 With H. G. Bungenberg de long and D. R. Kreger. Tissues of pris- matic cells containing biocolloids. I. Proc. K. Ned. Akad. Wet.. 43:512-21. With H. G. Bungenberg de {on". Tissues of prismatic celloidin cells containing biocolloids. II. Coacervation of gum-arable by toluidin-blue and the phenomena accompanying the dissolu- tion of the coacervate. Proc. K. Ned. Akad. Wet., 43:728-31. 1942 With H. P. Wolvekamp, G. P. Baerends, and W. F. H. M. Mom- maerts. O2 and CO2-binding properties of the blood of the cuttlefish (Sepia officinal~s) and common souid (Loli~o vulgarism. Arch. Neerl. Physiol., 26:203 -11. ~ ~ ~ ~ , With H. G. Bungenberg de long. Tissues of prismatic cells con- taining biocolloids. IV. Morphological changes of the complex coacervate gelatin + gum arabic in consequence of a pH change of the medium flowing along the membrane. Proc. K. Ned. Akad. Wet., 45:51-58. With H. B. Bungenberg de {on". Tissues of prismatic cells contain- ing biocolloids. V. Morphological changes of the complex coac- ervate gelatine-gum arabic owing to the addition of salts resp. non-electrolytes to the liquid flowing past the membrane. Proc. K. Ned. Akad. Wet., 45 :67-75. With H. G. Bungenberg de long. Tissues of prismatic celloidin cells containing biocolloids. VII. Stagnation effects. Proc. K. Ned. Akad. Wet., 45:204-5. 1948 A critical consideration of the quantum yield of Chlorella photosyn- thesis. Ph.D. dies., University of Utrecht. (Also in: Enzymologia, 13: 1-56.) 1949 On the interrelation of respiration and photosynthesis in green plants. Biochim. Biophys. Acta, 3:625-31.

40 BIOGRAPHICAL MEMOIRS 1951 Photo-induced interactions in metabolism of green plant cells. Symp. Soc. Exp. Biol., 5:211-21. 1952 On the efficiency of Chlorella growth. Acta Bot. Neerl., 1 :445-67. Photosynthesis in flashing light. Carnegie Inst. Washington Yearb. 51: 138-39. Efficiency of photosynthesis. Carnegie Inst. Washington Yearb., 51: 148-50. 1953 With E. C. Wassink and I. L. P. van Oorschot. The efficiency of light-energy conversion in Chlorella cultures as compared with higher plants. In: Algal Culture from Laboratory to Pilot Plant, ed. I. S. Burlew. Carnegie Inst. Washington Publ., 600:55-62. Experiments on photosynthesis by Chlorella in flashing light. In: Algal Culture from Laboratory to Pilot Plant, ed. i. S. Burlew. Car- negie Inst. Washington Publ., 600:63-75. With G. W. Veltkamp and W. P. Gelderman. On differential mano- and volumetric methods. Biochim. Biophys. Acta, 11:7-16. 1954 Kinetic studies of photosynthesis using a recording volumeter of extreme sensitivity. Congr. Int. Bot. Rapp. Commun. (8th), pp. 9-10. With I. L. P. van Oorschot. Improved yields in algal mass cultures. Acta Bot. Neerl., 3:533-46. 1955 Some sensitive and recording volumeters. Biochim. Biophys. Acta, t 16:35-44. 1956 With C. I. P. Spruit. High initial rates of gas exchange in respiration and photosynthesis of Chlorella. Biochim. Biophys. Acta, 19:212-23. With C. I. P. Spruit. Simultaneous observations of oxygen and car- bon dioxide exchange during non-steady state photosynthesis. Biochim. Biophys. Acta, 19:417-24.

BESSEL KOK 141 On the inhibition of photosynthesis by intense light. Biochim. Bio- phys. Acta, 21:234 - 44. Licht und Pflanzen. Strahlentherapie, 101:563-68. With J. A. Businger. Kinetics of photosynthesis and photoinhibi- tion. Nature, 177: 135-36. On the reversible absorption change at 705 m in photosynthetic organisms. Biochim. Biophys. Acta, 22:399-401. 1957 Absorption changes induced by the photochemical reaction of photosynthesis. Nature, 179:583 -84. Light induced absorption changes in photosynthetic organisms. Acta Bot. Neerl., 6:316 -36. Changes of absorption spectrum induced by illumination and their bearing on the nature of the photoreceptor of photosynthesis. In: Proceedings of the Second Photobiology Congress, Turin, Italy, pp. 369-83. Turin: Edizioni Minerva Medical With C. l. P. Spruit and l. A. Businger. Report on some results at Wageningen. In: Research in Photosynthesis, ed. H. Gaffron, A. H. Brown, C. S. French, R. Livingston, E. I. Rabinowitch, B. L. Strehler, and N. E. Tolbert, pp. 353-65. New York: Intersci- ence. 1958 Enige voorbeelden van bet gebruik van tracers in bet fotosynthese- onderzoek. Landbouwkd. Tijdschr., 70:334-43. 1959 Light induced absorption changes in photosynthetic organisms. II. A split-beam difference spectrophotometer. Plant Physiol., 34: 184-92. With I. M. Olson. Is oxidized bacteriochlorophyll an intermediate in bacterial photosynthesis? Biochim. Biophys. Acta, 32:278- 80. 1960 Efficiency of photosynthesis. In: Encyclopedia of Plant Physiology, ed. W. Ruhland, vol. 5, pp. 566 - 633. Berlin: Springer-Verlag. With W. Gott. Activation spectra of 700 ma absorption changes in photosynthesis. Plant Physiol., 35:802-8.

142 BIOGRAPHICAL MEMOIRS 1961 With G. Hoch. Spectral changes in photosynthesis. In: Light and Life, ed. W. D. McElroy and B. Glass, pp. 397-416. Baltimore: Johns Hopkins Press. Partial purification and determination of oxidation reduction po- tential of the photosynthetic chlorophyll complex absorbing at 700 mu. Biochim. Biophys. Acta, 48:527-33. With G. Hoch. Photosynthesis. Annul Rev. Plant Physiol., 12: 155- 94. With M. Gibbs and C. C. Black. Factors affecting CO2 fixation by chloroplasts. Biochim. Biophys. Acta, 52:474-77. With L. H. Bongers. Radiation tolerances in photosynthesis and consequences of excesses. In: Medical and Biological Aspects of the Energies of Space, pp. 299-322. New York: Columbia University Press. 1962 With H. Beinert and G. Hoch. The light induced electron para- magnetic resonance signal of photocatalyst P700. Biochem. Bio- phys. Res. Commun., 7:209-12. With H. Beinert. Light induced EPR signal of photocatalyst P700. II. Two light effects. Biochem. Biophys. Res. Commun., 9:349- 54. Light conversion in photosynthesis. In: Biologistics for Space Systems Symposium, pp. 83 - 104. AMRL-TDR-62-116. Dayton, Ohio: Wright Patterson AFB. 1963 With G. Hoch. A mass spectrometer inlet system for sampling gases dissolved in liquid phases. Arch. Biochem. Biophys., 101:160- 70. With G. Hoch and O. V. H. Owens. Photosynthesis and respiration. Arch. Biochem. Biophys., 101: 171-80. With G. Hoch and B. Cooper. Sensitization of chloroplast reactions. I. Sensitization of reduction and oxidation of cytochrome c by chloroplasts. Plant Physiol., 38 :274-79. With B. Cooper and L. Yang. Electron transport in chloroplast reactions. In: Studies on Microalgae and Photosynthetic Bacteria, pp.

BESSEL KOK 143 373-96. (Special issue, Plant Cell Physiol.) Tokyo: University of Tokyo Press. Significance ofP700 as an intermediate in photosynthesis. In: Pro- ceedings of the Fifth International Congress of Biochemistry. vol. 6. pp.73-81. ~ J Photosynthetic electron transport. In: Photosynthetic Mechanisms in Green Plants. NAS-NRC Publ., 1145:35 - 44. Fluorescence studies. In: Photosynthetic Mechanisms in Green Plants. NAS-NRC Publ., 1145:45 -55. With H. Beinert. Relationship between light induced EPR signal and pigment P700. In: Photosynthetic Mechanisms in Green Plants. NAS-NRCPubl.,1145:131-37. With G. Hoch. The photoreactions of photosynthesis. In: La Pho- tosynthese. Colloq. Int. CNRS, 119:93 - 107. With G. Hoch and O. V. H. Owens. Oxygen metabolism in Anacystas nidulans. In: La Photosynthese. Colloq. Int. CNRS, 119:261 - 72. 1964 With H. I. Rurainski and E. A. Harmon. Photo-oxidation of cyto- chromes c, f, and plastocyanin by deterrent treated chloro- plasts. Plant Physiol., 39:513-20. With L. Bongers. Life support systems for space missions. Dev. Ind. Microbial., 5:183-95. With H. Beinert. An attempt at quantitation of the sharp light- induced electron paramagnetic resonance signal in photosyn- thetic materials. Biochim. Biophys. Acta, 88:278-88. 1965 With H. I. Rurainski. Plastocyanin photo-oxidation by detergent- treated chloroplasts. Biochim. Biophys. Acta, 94:588-90. With E. B. Gassner and H. J. Rurainski. Photoinhibition of chlo- roplast reactions. Photochem. Photobiol., 4:215-27. Photosynthesis: The path of energy. In: Plant Biochemistry, ed. I. E. Varner and I. Bonner, pp. 903-60. New York: Academic Press. With H. l. Rurainski and O. V. H. Owens. The reducing power generated in photoact I of photosynthesis. Biochim. Biophys. Acta, 109:347-56. With E. A. Datko. Reducing power generated in the second pho- toact of photosynthesis. Plant Physiol., 40:1171-77.

44 BIOGRAPHICAL MEMOIRS 1966 Concentration and normal potential of primary photo-oxidants and reductants in photosynthesis. In: Currents in Photosynthesis, ed. I. P. Thomas and I. C. Goedheer, pp. 383-92. Rotterdam: Ad. Donker. With L. W. Jones. Photoinhibition of chloroplast reactions. I. Ki- netics and action spectra. Plant Physiol., 41:1037-43. With L. W. {ones. Photoinhibition of chloroplast reactions. II. Mul- tiple effects. Plant Physiol., 41:1044-49. With S. Malkin. Fluorescence induction studies in isolated chloro- plasts. I. Number of components involved in the reaction and quantum yields. Biochim. Biophys. Acta, 126:4 1 3-32. With G. M. Cheniae. Kinetics and intermediates of the oxygen evo- lution step in photosynthesis. In: Current Topics in Bioenergetics, ed. D. R. Sanadi, vol. 1, pp. 1-44. New York: Academic Press. With H. i. Rurainski. Long-wave absorption and emission bands in chloroplast fragments. Biochim. Biophys. Acta, 126:584-87. The rate-limiting reaction in photosynthesis. In: Conference on Bio- regenerative Systems. NASA Spec. Publ., 165: 1 1 1-15. With S. Malkin, O. Owens, and B. Forbush. Observations on the reducing side of the O2-evolving photoact. In: Energy Conversion by the Photosynthetic Apparatus. Brookhaven Symp. Biol., 19:446- 59. 1967 With I. E. Varner. Extraterrestrial life detection based on oxygen isotope exchange reactions. Science, 155: 1 1 10-12. With I. E. Varner. Extraterrestrial life detection by means of iso- topic oxygen exchange. Life Sci. Space Res., 5:206-16. Photosynthesis physical aspects. In: Harvesting the Sun Photosyn- thesis in Plant Life, ed. A. San Pietro, F. A. Greer, and T. I. Army, pp. 29-48. New York: Academic Press. 1968 With P. {oliot and A. Eliot. Analysis of the interactions between the two photosystems in isolated chloroplasts. Biochim. Bio- phys. Acta, 153:635-52. With B. Forbush. Reaction between the primary and secondary

BESSEL KOK 145 acceptors of photosystems of photosynthesis. Biochim. Biophys. Acta, 162:243-53. 1969 Photosynthesis. In: The Physiology of Plant Growth and Development, ed. M. B. Wilkins, pp. 335-79. New York: McGraw-Hill. With P. Eliot and M. P. McGloin. Electron transfer between the photoacts. In: Progress in Photosynthesis Research, ed. H. Metzner, pp. 1042-46. Tubingen: International Union of Biological Sci- ences. With C. Sybesma. Photosynthetic electron transport induced by flashing light in the purple photosynthetic bacterium Rhodospi- rallum rubrum. Biochim. Biophys. Acta, 180:410-13. 1970 With B. Forbush and M. McGloin. Cooperation of charges in pho- tosynthetic oxygen evolution. I. A linear four-step mechanism. Photochem. Photobiol., 11:457-75. With T. V. Marsho. Interaction between electron transport com- ponents in chloroplasts. Biochim. Biophys. Acta, 223:240-50. 1971 With T. V. Marsho. Detection and isolation of P700. In: Methods in Enzymology, vol. 23, Photosynthesis, Part A, ed. A. San Pietro, pp. 515-22. New York: Academic Press. With R. Radmer. A unified procedure for the detection of life on Mars. Science, 174:233-39. With B. Forbush and M. P. McGloin. Cooperation of charges in photosynthetic oxygen evolution. II. Damping of flash yield os- cillation, deactivation. Photochem. Photobiol., 14: 307-21. 1972 With K. L. Zankel. Estimation of pool sizes and kinetic constants. In: Methods in Enzymology, vol. 24, Photosynthesis and Nitrogen Fix- ation, Part B. pp. 218-38. New York: Academic Press. With W. W. Doschek. Photon trapping in photosystem II of pho- tosynthesis the fluorescence rise curve in the presence of DCMU. Biophys. I., 12 :832-38. With R. Radmer. An integrated multi-purpose biology instrument

46 BIOGRAPHICAL MEMOIRS utilizing a single detector, the mass spectrometer. Life Sci. Space Res., 10:211-25. Efficiency of photosynthesis. In: Horizons of Bioenergetics, ed. A. San Pietro and H. Gest, pp. 153-70. New York: Academic Press. 1973 O2 evolution in photosynthesis. In: Proceedings of the Second Inter- national Symposium on Oxidases and Related Redox Systems, ed. T. E. King, H. S. Mason, and M. Morrison, pp. 701-13. Baltimore: University Park Press. With R. Radmer. A kinetic analysis of the oxidizing and reducing sides of the O2-evolving system of photosynthesis. Biochim. Bio- phys. Acta? 314:28-41. Photosynthesis. In: Proceedings of the Workshop on Bio-Solar Conver- sion, Bethesda, Maryland, pp. 22-30. Washington, D.C.: Na- tional Science Foundation. 1974 With T. V. Marsho. Photosynthetic regulation by cations in spinach chloroplasts. Biochim. Biophys. Acta, 333:353-65. With R. Radmer. Kinetic observation of the system II electron pool isolated by mercuric ion. Biochim. Biophys. Acta, 357:177-80. With C. F. Fowler. Proton evolution associated with the photo- oxidation of water in photosynthesis. Biochim. Biophys. Acta, 357:308-18. With R. Radmer and C. F. Fowler. Electron transport in photosys- tem II. In: Proceedings of the Third International Congress on Pho- tosynthes~s Research, ed. M. Avron, pp. 485-96. Amsterdam: E1- sev~er. 1975 With P. Eliot. Oxygen evolution in photosynthesis. In: Bioenergetics of Photosynthesis, ed. Govindjee, pp. 387-412. New York: Aca- demic Press. With R. Radmer. Energy capture in photosynthesis. Annul Rev. Biochem., 44:409-33. Prospects of photosynthetic energy production. Sci. Technol., 35:519-26.

BESSEL KOK 147 With I. P. Martin, R. D. Johnson, and R. Radmer. Unified Mars life detection system. I. Astronaut. Sci., 23 :99-119. 1976 Photosynthesis: The path of energy. In: Plant Biochemistry, 3d ea., ed. J. Bonner and J. E. Varner, pp. 845-85. New York: Aca- demic Press. Prospects of photosynthetic energy production. In: The Current State of Knowledge of Photochemical Formation of Fuel, ed. N. N. Lichtin, pp. 133-39. Boston University Press. With R. Radmer. Energy requirements of a biosphere. In: Chemical Evolution of the Giant Planets, ed. C. Ponnamperuma, pp. 183- 97. New York: Academic Press. With R. Radmer. Mechanisms in photosynthesis. In: Chemical Mech- anisms in Bioenergetics, ed. D. R. Sanadi, pp. 172-220. American Chemical Society Monograph no. 172. Washington, D.C. With C. F. Fowler. Determination of H+/e- ratios in chloroplasts with flashing light. Biochim. Biophys. Acta, 423:510-23. With R. Radmer and i. P. Martin. System for biological and soil chemical tests on a planetary lander. I. Spacecr. Rockets, 13:719-26. With R. Radmer. Photoreduction of O2 primes and replaces CO2 assimilation. Plant Physiol., 58:336-40. With H. Hardt. Stabilization by glutaraldehyde of high-rate elec- tron transport in isolated chloroplasts. Biochim. Biophys. Acta, 449: 125-35. 1977 With R. Radmer. Light conversion efficiency in photosynthesis. In: Encyclopedia of Plant Physiology, n.s., ed. A. Trebst and M. Avron, vol. 5, pp. 125 - 35. Berlin: Springer-Verlag. With R. Radmer. Photosynthesis: Limited yields, unlimited dreams. Bioscience, 27:599-605. With B. Velthuys. Present status of the O2 evolution model. In: Research in Photobiology, ed. A. Castellani, pp. 111-19. New York: Plenum Publishing Co. With H. Hardt. Plastocyanin as the possible site of photosynthetic electron transport inhibition by glutaraldehyde. Plant Physiol., 60:225-29.

148 BIOGRAPHICAL MEMOIRS With B. Velthuys. Observations on the O2 evolution system. In: Proceedings of the Fourth International Congress on Photosynthesis, ed. D. O. Hall, I. Coombs, and T. W. Goodwin. on. 397-407. London: The Biochemical Society. 1978 ' 1 ~ With B. Velthuys. Photosynthetic oxygen evolution from hydrogen peroxide. Biochim. Biophys. Acta, 502:211-21. With R. Radmer and O. Ollinger. Kinetics and apparent Km of oxygen cycle under conditions of limiting carbon dioxide fixa- tion. Plant Physiol., 6 1:9 15-1 7. With H. Hardt. Comparison of photosynthetic activities of spinach chloroplasts with those of mesophyll and corn bundle sheath tissue. Plant Physiol., 62:59-63. With I. H. Goldbeck. Further studies of the membrane-bound iron- sulfur proteins and P700 in a photosystem I subchloroplast par- ticle. Arch. Biochem. Biophys., 188:233-42. With I. H. Goldbeck and B. R. Velthuys. Evidence that the inter- mediate electron acceptor, As, in photosystem I is a bound iron- sulfur protein. Biochim. Biophys. Acta, 504:226-30. With C. Waslien, I. Myers, and W. Oswald. Photosynthetic single- cell protein. In: Protein Resources and Technology: Status and Re- search Needs, ed. M. Milner, N. S. Scrimshaw, and D. I. C. Wang, pp. 522 - 42. Westport, Conn.: AVI Publishing Co. <A 1979 With l. H. Goldbeck. Redox titration of the electron acceptor Q and the plastoquinone pool in photosystem II. Biochim. Bio- phys. Acta, 547:347-60. With R. Radmer. Rate-temperature curves as an unambiguous in- dicator of biological activity in soil. Appl. Environ. Microbiol., 38:224-28.

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This distinguished series contains the biographies of deceased members of the National Academy of Sciences and bibliographies of their published works. Each biographical essay was written by a member of the Academy familiar with the professional career of the deceased. A cumulative index for all 57 volumes is now included. For historical and bibliographical purposes, these volumes are worth returning to time and again.

Volume 57 includes biographies of: Arthur Francis Buddington, J. George Harrar, Paul Herget, John Dove Isaacs III, Bessel Kok, Otto Krayer, Rebecca Craighill Lancefield, Harold Dwight Lasswell, Jay Laurence Lush, John Howard Mueller, Robert Franklin Pitts, John Robert Raper, Karl Sax, Gerhard Schmidt, Leslie Spier, Hans-Lukas Teuber, and Warren Weaver.

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