CYCLIC ANDNONCYCLIC PHOTO PHOSPHORYLATION 



189 



should stop when DPN is completely reduced. But such a DPN- depen- 

 dent formation would not be expected if the ATP formed in the experi- 

 ments represented by Tables 8 and 9 is the result of a DPIP-catalyzed 

 cyclic photophosphorylation. 



Fig, 3 shows a dependence of ATP formation on DPN availability 

 that is consistent with the mechanism of noncyclic photophosphoryla- 

 tion, A limited amount of DPN (0,3/imoles) was used as the electron 



10 20 30 40 

 minutes 



50 



Fig. 3. Dependence of noncyclic photophosphorylation on DPN. The re- 

 action mixture contained, in a final volume of 3 ml, 1 mg hexokinase, 10 

 ^g antimycin A, chromatophores (containing 45 /ig bacteriochlorophyll) 

 and the following (in/Umoles): tris buffer, pH 7.9, 100; magnesium chloride, 

 5; ADP, 0.5; K2HP3204, 10; sodium ascorbate, 20; 2,6-dichlorophenol 

 indophenol,0.2; DPN, 0.3. Additional DPN (2 /^moles) or a DPN regenerat- 

 ing system (lactate dehydrogenase plus 10 /imoles sodium pyruvate) was 

 added at the time indicated by arrow. 



