AEROBIC PHOSPHORYLATION IN R. RUBRUM 171 



TABLE 2 

 Effects of Antibiotie Inhibitors on Aerobie Phosphorylation 



The procedure followed and the enzyme preparation used were the same as 

 in Table 1. Ethanolic solutions of the antibiotics were added to the incubation 

 mixtures (final ethanol concentration, 0.5%). 



sucrose density gradient centrifugation of crude photosynthetic ex- 

 tract. 



The rates of both oxidation of DPNH and phosphorylation were 

 constant during the incubation period (Fig. 5), with a calculated P/2e 

 ratio of 0.45. This ratio is of the same order as that obtained with 

 washed crude 145,000 x g particles in earlier experiments (1), In 

 separate experiments it has been observed that the rate of DPNH oxi- 

 dation is independent of the presence of necessary components of 

 phosphorylation, viz.. Pi, Mg, and ADP, 



In a study of inhibitors of aerobic phosphorylation (Table 2), in- 

 hibitory concentrations of the antibiotics antimycin A, Valinomycin, 

 and Dianemycin were one to two orders of magnitude above those 

 effective in sensitive mitochondrial systems (6,7). On the other hand, 

 Oligomycin exerted an effect at a concentration required for inhibition 

 of mitochondrial phosphorylation (6) , 



It is of interest to note (Table 3) that aerobic phosphorylation was 

 inhibited by low concentrations of a carbonyl cyanide phenylhydrazone 

 derivative (lO-'^-lO'^ m), a potent uncoupling agent of mitochondrial 

 oxidative phosphorylation (8); on the other hand, the system was only 

 partially affected by dinitrophenol. In separate experiments, the DPNH 



