669 



Martin Gibbs 



Ik 

 Table 3- PERCENT DISTRIBUTION OF C IN GLUCOSE 



POLYSACCHARIDE AFTER FEEDING OF LABELED SUGARS TO 



C. pyrenoidosa and T. tenuis 



Substrate 



glucose-l-C^2i 

 glucose-2-C,. 



glucose-6-C,2^ 



glucose-l-C,K 



glucose-2-C,K 



glucose-6-C. 



ribose-1-C 



After 2 hours of incubation with the labeled substrates, it is 

 evident that Chlorella which contains aldolase converts glucose 

 to triose phosphates and back to polysaccharide via the Embden- 

 Meyerhof pathway. The distribution of isotope suggest that the 

 blue-green alga which does not contain aldolase possesses an 

 extremely active pentose-P cycle. Limited equilibration between 

 the two halves of the glucose molecule in Tolypothrix in con- 

 trast to Chlorella is taken as further evidence of a lack of 

 aldolase in the blue- green cell. On the other hand, an extremely 

 rapid pentose-P cycle together with an active glyceradehyde-3-P 

 oxidizing system could prevent the reformation of fructose-1,6- 

 diP from glyceraldehyde-3-P. Structural differences between the 

 two kind of algae may effect the handling of the labeled sugars. 

 The Chlorophyceae algae possess a definite chloroplast and mito- 

 chondria. In contrast, the Myxophyceae are the only algae in 

 which the pigments are not centered in definite chromatophores 

 and in which typical mitochondria type structures are not evident. 

 However, enzymes of the pentose-P cycle and Embden-Meyerhof path- 

 ways are not usually associated with cellular particulate matter. 



Studies with isolated chloroplasts 



The pioneering work of Arnon and his associates indicated that 

 the isolated chloroplast might afford a useful technique in 

 elucidating the nature of asymmetry in the reductive pentose-P 

 cycle. Arnon et al. had provided evidence that both the 

 intact chloroplast and reconstituted chloroplast system had a 

 complete and functioning cycle,. This conclusion was based essen- 

 tially on the appearance of C in some compounds of the cycle 

 after light- induced C Op uptake. Since the C can spread to a 

 number of compounds by a series of reactions which do not neces- 

 sarily constitute a cycle, its appearance in a few compounds of 

 the reductive pentose-P cycle is only suggestive evidence that a 



