THE EXPERIMENTS OF THE CHICAGO GROUP 



1649 



into the two other fractions could be stopped by the removal of air, showing 

 that it is associated with respiration. 



When algae were exposed to C*02 in light, the amounts of tracer fixed 

 were much larger than those taken up in the dark; furthermore, they cor- 

 responded to the manometrically observed carbon dioxide uptakes, indi- 

 cating that isotopic exchange reactions could be disregarded, at least in 

 the explanation of the origin of the main tagged products. 



en 



_i 

 _i 



UJ 



o 



"5. 



q: 

 iij 



Q. 

 CD 



z 

 o 



o 



< 



IT 



O 



20 40 60 



TOTAL ASSIMILATION, /il. COg PER /xl. CELLS 



Fig. 36.9. Relation between C* in fraction B and CO2 up- 

 take by photosynthesis (after Brown, Fager, and Gaffron 

 1949). 



As mentioned above, the tagged products were divided into three frac- 

 tions: one fraction (C), insoluble in aqueous alcohol, formed 78% of the 

 total dry weight, and contained chiefly proteins and polysaccharides. Of 

 the two fractions soluble in aqueous alcohol, one — fraction A, 21% of 

 dry weight — was soluble also in benzene ; it contained pigments and other 

 lipophilic constituents. The second one — fraction B — was insoluble in 

 benzene; it formed only about 1% of dry weight. As in dark fixation, 

 all C* was first taken up in fraction B, and subsequently distributed over 

 all three fractions (fig. 36.7). However, while the redistribution of C* 

 taken up (aerobically) in the dark occurred rapidly in the dark, the redis- 



