The Path of Carbon in Photosynthesis

Very little progress was made on this aspect of photosynthesis before isotopic carbon became available. Carbon balance studies had shown that the amount of carbon dioxide that went into a leaf could be almost entirely recovered in the sugars and starch fraction. However, there was no information regarding the steps involved in these transformations. Early studies (40) with the short-lived carbon isotope C indicated that during photosynthesis the tracer was fixed principally in the carboxyl group of a complex molecule that contained a number of hydroxyl and carboxyl groups. When the long-lived carbon isotope C became available in 1945, these studies were extended by workers in a number of different laboratories. 

in Photosynthesis in Plants (J. Franck and W. E. Loomis, eds.), p. 365. Iowa State College Press, Ames, 1949. 

The evidence for the participation of D-ribulose 1,5-diphosphate as a C02-acceptor in photosynthesis came from several sources. First, the data 

Alcohol-Soluble Compounds Found in Soybean Leaves Following A 10-Second Period of Photosynthesis 

and Mg ions. Subsequent work 53a) has shown that D-ribose 5-phosphate is converted to D-ribulose 1,5-diphosphate by the action of ATP and two enzymes, phosphoriboisomerase and phosphoribulokinase. Both of these enzymes were isolated and purified from spinach extracts. 

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M. Calvin, The path of carbon in photosynthesis, Nobel Lectures in Chemistry 1942 - 62, Elsevier, Amsterdam, 1964, 618-44. 

Benson, A.A. (2002) Following the path of carbon in photosynthesis a personal story—history of photosynthesis. Photosynth. Res. 73,31-49. 

The cycle of reactions that converts carbdh dioxide to carbohydrates is called the Calvin cyde, after M. Calvin, who received the Nobel Prize in chemistry in 1961 for his work on determining the path of carbon in photosynthesis. 

J. A. Bassham and M. Calvin, The Path of Carbon in Photosynthesis. Prentice-Hall, Englewood Cliffs, New Jersey, 1957. 

Calvin (1911-1997),278 after graduate education at the University of Minnesota and post-doctoral work with Polanyi at Manchester, was appointed to the faculty at Berkeley in 1937 and spent the rest of his career there. From purely physical organic work, he moved into bio-organic chemistry. He was awarded the Nobel Prize in 1961 for his work on the path of carbon in photosynthesis. Among the other physical organic chemists associated with Berkeley is Andrew Streitwieser (b. 1927), whose autobiography has appeared in the ACS series.279... 

Gibbs, M. "Structure and Functions of Chloroplasts" Sprlnger-Verlag, Berlin, 1971 Calvin, M. and Bassham, J. A. "The Path of Carbon in Photosynthesis" Prentice-Hall, Englewood Cliffs, 1957. 

Research Associate and Assistant Director, Bio-Organic Group, Radiation Laboratory, University of California, Berkeley. Research on the Path of Carbon in Photosynthesis with Melvin Calvin (Nobel Laureate, 1961). 

Used the first available quantity of radioactive carbon, C-14, for study of the path of carbon in photosynthesis with Melvin Calvin after the end of the war. Developed the technique of identification by solvent partition for identification of radiolabeled products of photosynthesis. Discovered and identified the first product of photosynthesis, which over the world is produced at the rate of ten billion tons per year (Phosphoglyceric acid, with M. Calvin). 

Calvin is the man known to have unlocked the secrets of photosynthesis. Calvin received the 1961 Nobel Prize in chemistry for identifying the path of carbon in photosynthesis. Shortly thereafter he established the Chemical Biodynamics Division (now Structural Biology Division), which he directed for 20 years. 

Bassham JA, Benson AA, Kay LD, Harris AZ, Wilson AT, Calvin M (1954) The path of carbon in photosynthesis XXI. The cyclic regeneration of carbon dioxide acceptor. J Am Chem Soc 76 1760-1770... 

In Section 13.5 we learned that the isotope was used to determine the source of O2. The radioactive isotope helped to determine the path of carbon in photosynthesis. Starting with " C02, it was possible to isolate the intermediate products during photosynthesis and measure the amount of radioactivity of each carbon-containing compound. In this manner the path from CO2 through various intermediate compounds to carbohydrate could be clearly charted. Isotopes, especially radioactive isotopes that are used to trace the path of the atoms of an element in a chemical or biological process, are called tracers. 

Calvin, Melvin (1964). The Path of Carbon in Photosynthesis. In Nobel Lectures, Including Presentation Speeches and Laureates Biographies 1942-1962. New York Elsevier. 

Inspiration, competence, confidence, being in the right place at the right time and sheer luck can help toward success in any endeavor. In his unraveling of the path of carbon in photosynthesis, Melvin Calvin was blessed with them all. 

Their work attracted the attention of Ernest Lawrence, the founder and director of the Radiation Laboratory which was later to become pivotal in the Manhattan project and famous as a center for nuclear research and development. From his understanding of nuclear physics, Lawrence reasoned that there should exist a long-lived carbon isotope with a mass number of 14 which, if used as a tracer, would greatly aid such biochemical work. Early in 1940, in cans of ammonium nitrate solution used as a shield around Lawrence s cyclotron, Ruben and Kamen discovered 14C with a half-life of 5700 years. Minute though the quantities were, the two scientists, joined later by Andy Benson, began to use it in an exploration of the path of carbon in photosynthesis until the events of December 7,1941 put all such nonessential investigations on hold. 

We already know from our earlier mapping of the path of carbon in photosynthesis that we need not only a reducing agent for the reduction of carbohydrate but also, in addition, a rather specific type of chemical. Since we know the exact steps for carbon reduction, we were able to... 

Taking these points into consideration, we arrive at the net equation for the path of carbon in photosynthesis. 

If one has available a cyclotron then there is the possibility of using the radioactive isotope N, providing one can work quickly since its half-life is only 10 min. Although its use is limited it has proved possible to feed N for very short exposure times and to plot the data in the form of percentage of incorporated isotope in different compounds. This method of plotting was used by Calvin (1962) in elucidating the path of carbon in photosynthesis and... 

Ruben et al. first used radiocarbon in studies of the path of carbon in photosynthesis (1940). They found that CO2 fixation in the dark is greater following preillumination. This is in accord with the concept that CO2 fixation occurs by dark reactions which use relatively stable chemical species formed in the light. They discovered that the radioactive product formed from labeled CO2 after preillumination was a carboxylic acid. These findings suggested that the path of carbon reduction in photosynthesis might very well include CO2 fixation mechanisms similar to those found in nonphotosynthetic plant tissues. 

Calvin and Benson and their co-workers used the radioisotope method to study carbon reduction in photosynthesis (Calvin and Benson, 1948, 1949). They allowed the plants to photosynthesize intermediate compounds from C 02 for short periods of time (a few seconds) and under a variety of experimental conditions. The plants were then killed, stopping the biochemical reactions. The radioactive products in the plant material were analyzed and identified. A careful study was made to determine the amounts of radiocarbon incorporated into chemical substances as a function of the experimental conditions. From the results of this study, they were able to map the path of carbon in photosynthesis. 

After a time, several other sugar phosphates were identified. Most important among these were the seven-carbon compounds, sedoheptulose-7-phosphate (IX) and sedoheptulose-l,7-diphosphate (SDP) (X), and the five-carbon compounds, ribulose-l,5-diphos-phate (RuDP) (II) and ribose-5-phosphate (XI), xylulose-5-phosphate (XII), and ribulose-5-phosphate (I) (Benson, et al., 1952). The roles of these compounds in the path of carbon in photosynthesis became more clear after they had been degraded to locate the position of radiocarbon atoms within the individual molecules (Bassham et al., 1954). 

Calvin M, Benson AA (1949) The path of carbon in photosynthesis IV. The identity and sequence of the intermediates in sucrose synthesis. Science 109 140... 

Recall from Section 14.5 that the isotope was used to determine the source of O2 in this reaction. The radioactive isotope helped to determine the path of carbon in photosynthesis. Starting with it was possible to isolate the intermediate... 

Since 1940 many new techniques and methods have been applied to photosynthesis research. Isotope studies have been especially valuable in elucidating the path of carbon in photosynthesis. Advantage has been taken of new advances in the field of enzyme chemistry. It is the purpose of this section to outline the essential features of what is presently known about photosynthesis and to review the significance of some of the recent discoveries. 

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