KINETIC STUDIES 



1677 



Figures 36.16 to 36.20, taken from the first-named paper, show time 

 curves of the tagging of several compounds in Scenedesmus cells exposed to 

 C*02 during steady photosynthesis in saturating light, at 15-20° C. (The 

 ordinates are the radioactivities eluted from the paper chromatogram — 

 about }i of those measured by direct plating.) 



MINUTES 



Fig. 36.20. Course of C*02 incorporation in Scenedesmus in most important 

 early tagged compounds presented on common time and activity scales (Scenedes- 

 mus, 15° C, 10 ixl cells) (after Benson et al 1952). 



"reservoir" 



Figures 36.16 and 36.20 show clearly that no appreciable 

 exists between C*02 and PGA. Figure 36.16 does not preclude a similar, 

 direct C*02 incorporation in PPA. We have mentioned before arguments 

 against such an assumption, presented particularly by the Chicago inves- 

 tigators (Fig. 36.10), and suggesting that PPA is a secondary product, 

 rapidly equilibrated isotopically with PGA. 



