164 



1. lODOACETATE AND lODOACETAMIDE 



Sucrose "j 



or \ 



Polysaccharide J 



If 



glucose- 1-P 



glucose-6-P 



w 



I fructose-6-P[ 



gluconate-6-P 



[fructose-l,6-diP| 



I triose-P| 

 PI50 = 3-4 ^||r- 



[ 1, 3-diP-glycerate [ 



3., 



I 3-P-glycerate| 



glycolate 



-*- serine-P 



glycine 



phosphoenolpy ru vate 



pyruvate 



Imalate 1 

 alanine >■ 

 aspartate] 



Scheme 3. Photosynthetic carbon cycle and its relation to the EM pathway. 



plified form, the condensation of CO2 with ribulose-l, 5-diP forming 3-P- 

 glycerate via a keto acid intermediate. Both Mortimer (1960) and Kandler 

 et al. (1961) have presented evidence that this is not the whole story. First 

 the 3-PGDH of plants has been shown to be less sensitive to iodoacetate 

 than the mammalian enzyme (page 19), being inhibited significantly only 

 above 0.1 raM, whereas photosynthesis is affected strongly at much lower 

 concentrations. Second, the changes in the patterns of C^* incorporation do 

 not entirely correspond to a block solely at 3-PGDH. For these reasons 

 another pathway whereby the keto acid can form fructose- 1,6-diP more 



