Photosynthesis Work Wins Nobel Prize Dr. Melvin Calvin receives chemistry award for partial explanation of photosynthesis

The award of the 1961 Nobel Prize in Chemistry to Dr. Melvin Calvin of the University of California, Berkeley, cli­maxes more than 15 years of research on the many complex processes in­volved in photosynthesis. While the problem is complicated, the statement of it can be very simple: How does the plant store electromagnetic energy from sunlight in chemical form by con­

verting carbon dioxide and water into carbohydrates and molecular oxygen?

Dr. Calvin's interest in this problem that is central to all life goes back to 1936, when he spent his second post­doctoral year in England under Dr. Michael Polanyi at the University of Manchester. There, Dr. Calvin be­came interested in the newly discov­ered phthalocyanines. He used these

compounds as models to investigate the energy conversion process of chlo­rophyll.

This part of the photosynthesis puz­zle remains unsolved, although Dr. Calvin and his co-workers have made considerable progress. But the other part of the photosynthesis process, the way in which carbon dioxide is incor­porated into the life cycle of the plant, has been worked out in detail by Dr. Calvin and his group since 1945. The success of this work can be at­tributed, in part at least, to the de­velopment of powerful new techniques and to the availability of ample quan­tities of radioactive carbon-14 for tracer studies.

Tracer Studies. Shortly after the end of World War II, the late Dr. G. N. Lewis offered Dr. Calvin space in the University of California's Law­rence Radiation Laboratory for work on the photosynthesis problem with carbon-14. Basically, Dr. Calvin's ap­proach has been to introduce radio­carbon in the form C 1 4 0 2 into the plant and then study the kinetics of the formation of various compounds containing C14 as a function of time of photosynthesis and other variables.

Much of his work has been carried out with suspensions of a unicellular green alga, Chlorella pyrenoidosa. At a particular time after the radiocarbon has been introduced into the system, he kills the algae by dropping them into hot alcohol and separates the com­pounds in the alcoholic extract by two-dimensional paper chromatography. He identifies the separated compounds by radioautography and measures them quantitatively by /^-particle counting with a thin-window Geiger-Muller tube.

Pathways. The pathways by which carbon atoms proceed from atmos-

Dr. Melvin Calvin Crisscrossed fields to pursue an idea

i

CH2o4

HC-OH

Xu5P / "iC-o® ATP

Malic Acid

Aspartic Acid

Alanine

P0 3 H Serine

Carbon Reduction Pathways in Photosynthesis Absorption of light by chlorophyll leads, in ways not yet understood in detail, to reactions producing the two key cofactors needed in the cycle. Triphosphopyridine nucleotide (TPN-{-) reacts with water to give the reduced form, TPNH. And adeno­sine diphosphate (ADP) reacts with inorganic phosphate to give the triphosphate (ATP). TPNH is a powerful reducing agent; the function of ATP is to carry chemical potential and act as a phosphorylating agent. Carbon dioxide enters the cycle (upper right) by reacting with ribulose-l,5,-diphosphate (RuDP) to give a highly labile /3-keto acid. This breaks down into 3-phosphoglyceric acid (3-PGA). Some molecules of 3-PGA are converted to products outside the cycle; others are re­duced, through the action of ATP and TPNH, to 3-phosphoglyceraldehyde. Next, five molecules of this triose phosphate are converted, by a variety of pathways, into three molecules of a pentose phosphate, ribulose-5-phosphate (Ru5P). To com­plete the cycle, the diphosphate, RuDP, is produced from Ru5P with the aid of ATP. The reactions in the cycle are enzymatically catalyzed. The sugar phos­phates (at left) are di hydroxy acetone phosphate (DHAP), fructose-l,6-diphosphate (FDP), fructose-6-phosphate (F6P), sedoheptulose-l,7-diphosphate (SDP), sedo-heptulose monophosphate (SMP), erythrose-4-phosphate (E4P), ribose-5-phosphate (R5P), and xylulose-5-phosphate (Xu5P).

36 C & E N NOV. 13, 1961

pheric carbon dioxide into the constit­uents of plant material include:

© Addition of carbon dioxide to a 2-ketopentose-l,5-diphosphate to give a labile 2-carboxy-3-ketopentose-l,5-diphosphate which splits to yield phos-phoglyceric acid.

® Reduction of this acid to a triose.

• Regeneration of the 2-ketopentose-1,5-diphosphate (ribulose diphos­phate) from the triose by a series of condensation and rearrangement reac­tions involving five-, six-, and seven-carbon sugars.

The net result of each complete turn of the cycle is incorporation of three molecules of carbon dioxide and the production of one three-carbon (or half of a six-carbon) organic molecule. This in turn requires six molecules of a reducing cofactor (reduced triphos-phopyridine nucleotide) and six mole­cules of adenosine triphosphate, which acts as a source of chemical energy. It is these two cofactors, and possibly others, that result in some manner from the absorption of light energy by chlorophyll.

Dr. Calvin, a strong believer in the value of cross-fertilization of scientific disciplines, points out that it took the special knowledge and abilities of sci­entists in a variety of areas—chemistry, biology, and physics—to unravel the many complicated problems encoun­tered in the study. Several years ago he said, "Our greatest future progress may lie in the hands of men who are willing and able to ignore the artificial classifications we have erected, men who will readily crisscross these fields in the pursuit of an idea/ '

Other Interests. In addition to his work in the carbon reduction cycle and the energy absorption mechanism in photosynthesis, Dr. Calvin's re­search interests include physical or­ganic chemistry, organic chelate com­pounds, and the problem of life's origin (C&EN, May 22, page 96).

Dr. Calvin was born in St. Paul, Minn., in 1911 and received his B.S. from Michigan College of Mining and Technology at Houghton in 1931. After obtaining his Ph.D. from the University of Minnesota in 1935, he spent two years in England on a Rockefeller Foundation grant as a postdoctoral fellow. In 1937 he joined the University of California as an in­structor, has been professor there since 1947 and director of the bio-organic chemistry group at the univer­sity's radiation laboratory since 1946.

Nobel Physics Award Goes to Californians Moessbauer, Hofstadter share prize for work on structure of matter

The 1961 Nobel Prize in Physics will be shared by two California physicists. Dr. Robert Hofstadter of Stanford Uni­versity was cited for his research on electron scattering in atomic nuclei and the information this has yielded on the structure of nucleons. Dr. Rudolf L. Moessbauer, senior research fellow at California Institute of Technology, shares the prize for research on the resonance absorption of gamma radia­tion and discovery of the Moessbauer effect.

Dr. Hofstadter showed that the atom's nucleus doesn't have a sharp boundary; rather it is characterized by a charge density constant for some dis­tance from the center but decreasing so that outer layers become more dif­fuse.

Each nucleon, Dr. Hofstadter found, has a dense meson core surrounded by two Yukawa clouds of mesons. In the proton, 28% of the positive charge is in the outer cloud, 60% is in the denser inner cloud, and the remaining 12% is in the pointlike core.

The two outer meson clouds in the neutron are the same as in the proton except that the inner cloud is negative.

Dr. Rudolf L. Dr. Robert Moessbauer Hofstadter

The positive core's charge plus the positive outer cloud's charge equals the negative charge of the inner cloud.

Dr. Hofstadter was born in 1915 and graduated from City College of New York in 1935. He received his Ph.D. from Princeton in 1938.

Moessbauer Effect. By anchoring a radioactive nucleus inside a crystal lattice so that it cannot recoil, Dr. Moessbauer found that gamma radia­tion is produced with sharply defined wave lengths. This effect has already been used to confirm Einstein's predic­tion that the frequency of a light beam

changes in a gravitational field. Dr. Moessbauer and his colleagues are cur­rently using this effect to study the internal magnetic and electric fields in isotopes of the rare earths.

Dr. Moessbauer, born in Munich, Germany in 1929, received his Ph.D. from the Technical Institute there.

New Assistant Director for Chemical Abstracts Service

Dr. Fred A. Tate

Dr. Fred A. Tate has been appointed assistant director of the American Chemical Society's Chemical Abstracts Service in Columbus, Ohio.

Dr. Tate will help direct CAS in providing an effective key to the world's chemical literature. In addi­tion, he will share responsibilities for all areas of internal operations, in­cluding organization, planning, policy administration, finance, personnel, and production management of the CAS's 11 operating departments.

Dr. Tate received a B.S. in mathe­matics in 1947 from Ohio University. He received an M.A. in 1950 and a Ph.D. in 1951 in organic chemistry from Harvard University. After two years as an assistant professor of chem­istry at Ohio University, he joined the staff of Chemical Abstracts Service as an assistant editor in the organic chemistry section, becoming associate editor in 1956. From 1957 to 1959, he was a staff assistant in the admin­istrative engineering department of General Motors Research Laboratories, Warren, Mich. In 1959 he became manager of the scientific information section of Wyeth Laboratories, Phila­delphia, Pa.

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