CYCLIC AND NONCYCLIC PHOTO PHOSPHORYLATION 187 



0.5 



S 0.4 



I 



^ 0.3 

 ^ 0.2 



I 



0.0 



TRANSHYDROGENASE ACTIVITY 

 in R. rubrum chroma tophores 



+0.05 /imofes 

 DPN 



Fig. 2. Transhydrogenase activity in R. rubrio)! chromatophores. The re- 

 action mixture contained, in a final volume of 3 ml, alcohol dehydrogenase, 

 chromatophores (containing 32 ^g bacteriochlorophyll) and the following 

 (in //moles): tris buffer, pH 7.9, 100; magnesium chloride, 5; ethanol, 170; 

 TPN, 2. Also present was 0.05 //moles DPN or extract (see text) as indi- 

 cated. The reaction was carried out in Thunberg type cuvettes at room 

 temperature in the dark. 



occurred in a complete system in which the photoreduction of DPN 

 was inhibited by the addition of the inhibitor phenyl mercuric acetate 

 (22). 



Stoichiometry 



The stoichiometry of the ATP formed and the DPN reduced in the 

 course of noncyclic photophosphorylation is shown in Table 9, The 

 theoretical ratio of ATP/DPNH2 = 1 was obtained when the DPNH2 

 formed was trapped by an added lactate dehydrogenase system. With- 

 out the lactate dehydrogenase system, the ratio ATP/DPNH2 was 



