THE EXPERIMENTS OF THE CHICAGO GROUP 



1647 



The earlier, contradictory results have not been satisfactorily explained. It was, 

 however, suggested that they might have been due to the pretreatment of the algae. To 

 exhaust all C( 12)02, prior to exposure to C( 14)02, the cells were made to photosynthe- 

 size for a long time without renewed supply of carbon dioxide; this could have depleted 

 them of all photosynthetic intermediates, and caused C(14) to spread practically instan- 

 taneously beyond the first fixation product (phosphoglyceric acid). It may be noted 

 here that Calvin could find no satisfactory explanation also for the failure of Ruben, 

 Kamen, and co-workers to identify any of the known respiration intermediates among 

 the product of brief photosynthesis in C(ll)02 (c/. Vol. I, page 242). 



■o-.^ 



20 



J I I L 



60 



40 - 



20 - 



B 



J I I I I 



b-^ 



'-' 20 40 60 



TIME, min 



Fig. 36.6. Distribution of C* fixed aerobically in the dark over fractions 

 A, soluble in aqueous alcohol and benzene; B, soluble in aqueous alcohol, 

 insoluble in benzene; and C, insoluble in aqueous alcohol, as function of time 

 (after Brown, Fager, and Gaffron 1949). 



Brown, Fager and Gaffron (1948, 1949) were aware of the complications 

 which may be caused by "respiratory" C*02 fixation. They therefore 



