Light- Induced Phosphorylation in Extracts of 

 Purple Sulfur Bacteria* 



JACK W. NEWTON and IMARTIN D. IvAMEN, Edward Mallinckrodt 

 Institute of Radiology, Washington Universitt/ Medical School, 



St. Louis, Missouri 



We have been studying the electron transport systems which may be 

 peculiar to the photosynthetic process in purple bacteria. The purple 

 sulfur bacterium Chromaiium sp., strain D, was selected for study 

 because it provided a system for investigating such processes in an 

 organism which photosynthesizes in the complete absence of a func- 

 tional aerobic metabolism. In Chromaiium, growth and photosyn- 

 thesis are obligately anaerobic processes. Aerobic oxidative proc- 

 esses do not appear to provide the cells with any biochemical energy 

 utilizable for growth. Recently, Dr. A. Frenkel has described a 

 light-induced phosphorylation of ADP to ATP in extracts made from 

 the photoheterotrophe Rhodospirillnm ruhrum. We have been able 

 to extend these observations to extracts made from Chromaiium and 

 to show that light induces the phosphorylation of ADP under strictly 

 anaerobic conditions. We have succeeded in partially purifying the 

 light phosphorylation system by differential centrifugation. The 

 Chromaiium extracts are not so active as the R. ruhrum preparations 

 in carrying out photophosphorylation, but extracts can be prepared 

 which form in the light about 0.5 urn of ATP per hour per milligram 

 protein. In contrast with the R. ruhrum extracts, Chromaiium prep- 

 arations invariably exhibit, in addition to the light effect, a dark 

 phosphorylation which appears to result from the fermentation of 

 endogenous reserves, since it can be reduced by anaerobic incubation 

 of the cells in buffer in the dark prior to preparation of the extracts. 

 Extracts of Chromnlium prepared by high-speed homogenization with 

 glass beads can be separated into a number of different fractions by 

 differential centrifugation. Centrifugation of crude extracts at 

 25,000 X g for 1 hour, sediments the bulk of the pigment containing 



* This work is made possible by the continued financial support of the C. F. 

 Kettering Foundation. 



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