THE ROLE OF MALIC ACID 



1669 



of carboxylation. Bassham et al. (1954) discussed two mechanisms that 

 could possibly account for the immediate appearance of tagged carbon 

 atoms in compounds not connected directly with the external C*02 reser- 

 voir. One of them is the possibility that some rapid enzymatic reactions 



10 20 JO 40 



Fig. 36.17. C*02 fixation in sedoheptulose phosphate, ribulose diphosphate, 

 and mannose phosphate as function of time. 10 pi. Scenedesmus cells, 20° C. 

 The separation of sedoheptulose and mannose is imperfect (both occurring in the 

 same general monophosphate area) (after Benson et al. 1952). 



ASPARTIC ACID 



10 to 30 40 SIC 



MINUTES 



Fig. 36.18. C*02 incorporation in some d compounds as function of time (10 

 All. Scenedesmus, 15° C). Insert shows the initial slope of the mahc acid tagging 

 curve (after Benson et al. 1952). 



could occur during (or after) the supposedly instantaneous and complete 

 stoppage of life processes by boiling alcohol, and could transfer some C* 

 atoms from the primary into the "secondary" products. The second 

 (rather vaguely described) possibihty is that of labelled C* "skipping" 



