acid is so synthesized in the cytoplasm, outside the chloro- 

 plasts. Within the chloroplasts, however, the appearance of 

 C^^ in malic acid in the very shortest exposures to C^*02 and 

 in the pre-illumination experiments (see Figure 5) indicate 

 that it is, in part at least, a product of Ci-Cs carboxylation 

 and reduction. 



Glycolic acid, acetic acid, and glyoxylic acid 



Even if acetate and glyoxylate are formed from malic 

 acid, there are probably other more important synthetic 

 routes from the carbon reduction cycle to these compounds. 

 Benson and Calvin (41) found that barley seedlings sub- 

 jected to 30 seconds photosynthesis with C^^02, followed by 

 2 minutes light without CO2, formed large amounts of C"- 

 labeled glycolic acid. Calvin et al. (14) and Schou et al. (42) 

 degraded glycolic acid and phosphoglyceric acid obtained 

 from barley leaves and from Scenedesmus that had photo- 

 synthesized for a few seconds in the presence of C^*02 or 

 HC^^Os". The alpha and beta carbon atoms of PGA were 

 found to be always about equal to each other in radioactivity 

 and always less than the carboxyl carbon until such time 

 (1 to 5 minutes) as all three carbon atoms were completely 

 labeled. The two carbon atoms of glycolic acid were always 

 about equal to each other in labeling. When C^*H20H 

 — COOH was administered to the unicellular algae Scenedes- 

 mus during 10 minutes photosynthesis with V2 per cent CO2 

 in air or N2, a pattern of photosynthetic intermediates was 

 found similar to that obtained during photosynthesis with 

 C^*02. Moreover, upon degradation of the PGA we found that 

 less than 10 per cent of the radioactivity was in the carboxyl 

 carbon. Clearly, glycolic acid is incorporated for the most part 

 into normal intermediates of the carbon reduction cycle with- 

 out preliminary conversion to CO2, since so little C^* was 

 found in the carboxyl carbon of PGA. However, alpha and 

 beta carbon atoms of the PGA were found to be equally 

 labeled. Thus the pathway from glycolic acid to the alpha and 



39 



