CYCLIC AND NONCYCLIC PHOTO PHOSPHORYLATION 193 



Chromatophores retained a capacity for cyclic photophosphorylation 

 even after extended storage but lost irreversibly the capacity for non- 

 cyclic photophosphorylation after storage for a few days. This loss 

 was associated with an inactivation of the DPN reducing system, 



Chromatophores, unlike chloroplasts, photoreduce DPN but not 

 TPN. However, chromatophores contain a DPNH2-TPN transhydro- 

 genase and photoreduce TPN in the presence of catalytic amounts of 

 DPN. 



The effect of ascorbate concentration was investigated in relation 

 to the use of dichlorophenolindophenol, methyl viologen and phenazine 

 methosulfate as "bypass agents" for cyclic photophosphorylation when 

 it was inhibited by antimycin A. 



Ascorbate, reduced DPN and H2 plus hydrogenase were compared, 

 in the presence and absence of dyes, as regulators of the oxidation- 

 reduction state during cyclic photophosphorylation. 



Cyclic photophosphorylation was found to be irreversibly inactivated 

 by a salt treatment at pH 5, 



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