BARHARA RE 1 RACK AND IRl IZ L/RMANN 



^v^l 



SH Effect on Photophosphorylation 

 and Photohydrolysis 







10 



20 



30 



40 



yuM cysteine/ 3 ml. 



Fig. .2. The action of cysteine on photophosphorylation of ADP and pliotohydroly- 

 sis of ATP in cell-free extracts of Anabaena variabilis. 



would subsequently be split to inorganic phosphate. The products 

 of ATP hydrolysis were examined in an assay mixture containing sub- 

 strate levels of ATP. The nucleotides contained in the TCA extract 

 were separated by paper electrophoresis in ammonium formate buffer 

 a^ pH 3.8, and spotted on the paper by ultraviolet quenching. Clearly 

 visible spots were found corresponding to ATP and ADP, but none 

 was detected at the level of the AMP marker. It is concluded that 

 ADP is the product of ATP hydrolysis. 



The similarity between ATP synthesis and hydrolysis with respect 

 to requirements and inhibitor effects suggests a close interrelationship 

 between these two light-induced reactions. It seems reasonable to 

 conclude, in fact, that the photohydrolysis is a reversal on the path- 

 way of photophosphorylation. To support such a proposition, we 

 felt obliged to demonstrate photohydrolysis in spinach chloroplasts, 

 since several laboratories have reported a complete absence of ATPase 

 in chloroplasts; the photohydrolysis was foimd, but it was necessary 

 to increase the cysteine concentration to 0.08 M. Furthermore, for 

 this purpose, pyruvic kinase purchased as an ammonium sulfate sus- 

 pension had to be dialyzed against 0.5 M KCl. Due to the presence 

 of ammonium ion, the usual amount of pyruvic kinase completely 

 inhibited photophosphorylation with spinach chloroplasts (7) , where- 

 as it had no effect with algal fragments. Table 4 demonstrates that 



