PHOTOSYNTHESIS 



5-phosphate. Although it is not possible to choose unequivocally 

 between these two possibilities at present, evidence obtained 

 from degradation of the various radioactive sugar phosphates 

 obtained from soy bean leaves which were exposed to G^^02 for 

 a very short time, indicates that the original proposal (as shown 

 in Figure 1) is correct. These degradation results are shown in 

 Table I, which is derived from Table I of reference 4 by assuming 

 that the carbon atoms numbers 1, 2, and 6 have the same C^^ 

 level as that found in carbon 7. 



TABLE I 



Distribution of C^^ in Sedoheptulose 

 Isolated from Soy Bean Leaf 



Time of exposure to G'^02, sec. 



H2C— OH 



c=o 



I 

 HO— C— H 



I 

 HC— OH 



I 

 HG— OH 



HC— OH 



H2G— OPO3H 



In either version for sugar rearrangement carbons numbers 4 

 and 5 of sedoheptulose are derived from carbons 3 and 4 of fructose, 

 respectively. However, in the original version (Figure 1) 

 carbon 3 of sedoheptulose is derived from the carbon 1 of 

 glyceraldehyde phosphate directly, whereas in the modified 

 version carbon 3 of sedoheptulose is derived from carbon 3 of 

 fructose and therefore should have the same labeling at all times 

 as carbon 4 of the sedoheptulose. Since this is not the case, the 

 original version of the rearrangement seems more likely, espe- 

 cially since at very short exposures of the plant to C"02, carbon 3 

 is much more highly labeled than carbon 4, as would be expected 



37 



