THE CHEMISTRY OF PHOTOSYNTHESIS 



139 



75. WiNOGRADOw, A. p. and Teis, R. V. : C. R. Acad. Sci. URSS, 33:490, 1941 ; 56-59 



1947. 



76. WiNTERM.ANS, .1. F. G. M.: Thesis, Wageningen, 1955. 



77. YosHiD.^, T. et al.: Acta Phytochim. {Japan), /J:13, 1942. 



C. INTERMEDIATE PRODUCTS OF PHOTOSYNTHESIS 



§ 53 The Carbon Cycle of Photosynthesis 



To establish the intermediate products of photosynthesis, Calvin et al. 

 (8, 9, 10, 19, 22) carried out a series of basic experiments with labeled CO2, 

 opening up new interesting ways of research. The results of similar experi- 

 ments have been published by Fager et al. (24). The test object Chlorella is 

 illuminated during 10 to 60 sec in an atmosphere of i^CO.. Then, the alga 

 is killed in hot 80% alcohol and the alcoholic extract examined by means 

 of paper chromatography and autoradiography. Even the first experiments 

 showed that the first products to appear were carbohydrates; and after longer 

 illumination the labeled carbon was also found in fats, amino-acids and pro- 

 teins. As will be discussed later, other investigators found different se- 

 quences, e.g., amino-acids before sugars. By steadily decreasing the time 

 of illumination, Calvin tried to trap the first CO2 fixadon product to appear; 

 this was considered to be 3-phosphoglyceric acid. The further reduction of 

 this substance to sugars was represented as follows: 



H2COPO3H, 

 HCOH 



*COOH 



3-phosphogly- 

 ceric acid 



+ 2H 

 — ■ — ■ — ■ *■ 



dehydrogenases 



H2COPO3H0 

 HCOH 



*CHO 



3-phosphogly- 

 ceraldehyde 



triose 



phosphate 

 isomerase 



H2COPO3H2 

 CO 



H2COPO3H2 



I 

 HCOH 



*CHO 



3-phosphogly- 

 ceraldehyde 



H2COPO3H 



3^.2 



+ 



CO 



*CH20H 



phosphodihy- 

 droxyacetone 



aldolase 



>■ 



*CH20H 



phosphodihy- 

 droxyacetone 



H2*COP03Ho 



I 

 CO 



HOCH 



I 

 HCOH 



HCOH 



H2*COP03H2 



fructose-l ,6- 

 diphosphate 



The condensation of two molecules triose phosphate is the reversal of the 

 anaerobic degradation of fructose-l, 6-diphosphate (§ 44). The distribution 

 of the radioactive isotope *C among the C atoms of 3-phosphoglyceric acid 

 and of fructose-l, 6-diphosphate shows that the CHO group of 3-phospho- 



