DANIEL I. ARNON 



527 



acetyl-CoA lioni acetate and coen/yine A. The activated compounds 

 then become ready lor {participation in the synthetic reactions that 

 are catalyzed by specific enzyme systems, all ol which function in the 

 dark. A summary of those reactions of ATP that have now been ex- 

 perimentally documented in the carbon metabolism of Chromatium 

 is given in Fig. 14. 



Evidence that the sole contribution of light in these reactions is 

 the formation of ATP was obtained by replacing light with a supply 

 of exogenous ATP and finding that carbon assimilation woidd then 

 proceed in the same manner in the dark as in the light (97) . Other 

 evidence for the ecjuivalence of light and ATP is given in Table G. 

 Here assimilation occmred either in the dark with added ATP or 

 in the light Avhen ATP was allowed to form photosynthetically. If, 

 hoAvever, the ATP which was formed in light was trapped by an added 

 hexokinase-glucose system, than acetate assimilation ceased. The ad- 

 dition of hexokinase alone, w'ithout glucose as the ATP acceptor, 

 was not inhibitory (Table 6) . 



The experimental substitution of ATP for light was considered 



ACETATE ASSIMILATION AND CARBOHYDRATE CYCLE IN CHROMATIUM 

 ATP< 



^ I 1 U Ul use - 3 



V 



ribulose di-P 

 GLUTAMATE 



Iriose -P 



itoconate 



t 



P-glycerate 



n 



DPN+Hj 

 ATP ASPARTATE 



ATP 



citramalote 



ATP 



P-enolpyruvate / oxolacelote / /AcCoAi^ — [ACETATE 



CO, 



ATP 



[ocetoidehyde]* COj 

 pyruvote ^-....^^ citrole 



Ac CoA '^ ^ALANINE 



2H 



I 



IacETATEI malote<— fumorate^ — ^ succinate <—isocitrate->o<-ketoglutorote — > GLUTAMATE 



ATP 





glyoxylate 



ACETATE —^^ Ac CoA 



Fig. 14. Reactions of carbon assimilation in Chromatium. Further details are 

 given by Losada, Trebst, Ogata, and Arnon (97). 



