PHOTOS YNTHE TIC PHOSPHORYLATION WITH 



BACTERIAL CHROMA TOPHORES: CATALYSIS 



BY A NATURALLY OCCURRING FACTOR 



(PHOSPHODOXIN)l 



C. C. BLACK and A. SAN PIETRO 



Charles F. Kettering Research Laboratory 

 Yellow Springs, Ohio 



A light- induced phosphorylation of ADP with cell-free preparations 

 from the photosynthetic bacterium Rhodospirillum ruhnim was first 

 observed by Frenkel (1-3). This light- induced process, which has 

 been termed photosynthetic phosphorylation, has subsequently been 

 observed with chromatophores from Chromatiiim (4-6) and Chloro- 

 hium (4), Photosynthetic phosphorylation by bacterial chromatophores 

 occurs in the absence of an exogenous electron acceptor at a rate 

 which is compatible with the growth rate of whole cells. This is in 

 sharp contrast to the low endogenous rate of photosynthetic phosphory- 

 lation with spinach chloroplasts (7,8), which is only one to two per 

 cent of the photosynthetic capacity of intact spinach leaves. Whereas 

 the endogenous rates observed with chromatophores and chloroplasts 

 are markedly different, both may be increased in the presence of suit- 

 able cofactors. For example, photosynthetic phosphorylation by 

 chromatophores and by chloroplasts is stimulated about 10-fold (5,9) 

 and as much as 2,000-fold (10). respectively, in the presence of the 

 dye methyl phenazoniummethosulfate. It seemed reasonable, therefore, 

 that the intact organism might contain some component (s) which 

 isolated chromatophores and chloroplasts either lacked or contained 

 in low concentration. Thus, a study of the natural factors involved in 

 photosynthetic phosphorylation was initiated. 



A water-soluble, heat-stable factor which stimulates the rate of 

 photosynthetic phosphorylation by spinach chloroplasts as much as 

 200-fold (8) has been isolated from both spinach leaves and chloro- 

 plasts. Further study revealed the presence of a similar factor^ in 

 many photosynthetic organisms, including bacteria (8). In this report, 



1 Contribution No. 116 of the Charles F. Kettering Research Laboratory. Sup- 

 ported in part by a research grant (GM 10129-01) from The National Institutes 

 of Health, U. S. Public Health Service. 



2 It is not known whether the factor isolated from different organisms is the 

 same or different. 



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