668 



Martin Gibbs 



in the glucose of the polysaccharide. These results and those of 

 Kandler and Richter suggest the following: (l) aldolase is 

 present in Anacystis and Chlorella and the reductive carbon cycle 

 functions in both organisms but the enzyme is not detected in 

 extracts of Anacystis for various reasons; (2) aldolase is not 

 involved with the conversion of COg to carbohydrate during photo- 

 synthesis; (3) different mechanisms of photosynthetic assimila- 

 tion of CO2 operate in the 2 algae but both mechanisms give rise 

 to the same distribution of C pattern. 



Feeding of labeled acetate and CO p in the dark 



It became of interest to determine whether asymmetry of label 

 in the glucose was a light-dependent event. It was found that 

 C^^Oo and acetate- l-C-'-^ given to Chlorella produced an asym- 

 metrically labeled glucose; in contrast, acetate-2-C-'-^ formed a 

 symmetrically labeled hexose (Table 2). 



Table 2. DARK INCORPORATION OF C Op, ACETATE-1-C , AND 



14 

 ACETATE-2-C INTO GLUCOSE OF C. pyrenoidosa 



Sub St. 



*k 



^ °2 11, 

 acetate-l-C,r 



acetate-2-C, . 

 acetate-2-C 



Light is apparently not necessary for the formation of 

 asymmetrically labeled glucose from COg. In the dark, the 

 labeled acetates are apparently incorporated into glucose by 2 

 super- imposed over-all mechanisms; a rapid one involving the 

 citric acid cycle and glycolytic pathway yielding symmetrically 

 labeled glucose and a slower operating carbon reduction cycle 

 which causes asymmetry. The conclusion can be drawn that asym- 

 metry is a property of the carbon reduction cycle and not of the 

 pathways leading to carbohydrate involving the reversal of 

 respiration^ -^5; . 



Feeding of labeled sugars 



To test whether asymmetry is characteristic of the reductive 

 carbon cycle or of respiratory pathways, specifically labeled 

 glucose and ribose were fed to algae. Further information of 

 carbohvdrate metabolism was obtained by using Chlorella pyrenoi - 

 dosa''-^^^ which contains aldolase and Tolypothrix tenuis which is 



lacking aldolase. 



