The Reactions of Rhodospirillum rubrum Extract 



with Cytochrome c 



LUCILE SMITH,* Molteno Institute, University of Cambridge, 



Cambridge, England 



The experiments reported investigated (a) the possible role in 

 the respiratory chain of the soluble cytochrome co which has been 

 isolated from the photosynthetic bacterium Rhodospirillum rubrum 

 (1) and (6) the reactions of extracts of the bacteria on illumination. 

 These experiments represent a continuation of the work of Duysens 

 (2), Vernon and Kamen (3-5), and Chance and Smith (6), which led 

 to the suggestion that one or more cytochromes may be oxidized or 

 reduced in a photochemical reaction. It was hoped that the experi- 

 ments might shed some hght on the oxidation-reduction reactions of 

 the cytochromes, as well as on the possible involvement of these 

 reactions in photosynthesis. 



DARK REACTIONS OF EXTRACTS OF RHODOSPIRILLUM 



RUBRUM 



An extract of Rhodospirillum rubrum was prepared by grinding 

 washed cells with powdered glass. This preparation showed oxygen 

 uptake on addition of a number of substrates. From this extract a 

 particulate fraction was isolated by high-speed centrifugation which 

 took up oxygen only on addition of succinate; the O2 of the particulate 

 suspension oxidizing succinate approached that of the whole cells. 

 Both the extract and the particles contained the chlorophyll and 

 carotenoids of the bacteria. 



When the extract (or particulate suspension) was added to reduced 

 mammalian cytochrome c or the bacterial cytochrome co in the dark, 

 a slow oxidation of the cytochrome was observed, as found by Vernon 

 and Kamen (3). The rate of oxidation of mammalian cytochrome c 

 was more rapid than that of the bacterial cytochrome C2. With the 



* Exchange fellow of the British and American Cancer Societies. Present 

 address: Johnson Foundation for Medical Physics, University of Pennsylvania, 

 Philadelphia, Pa. 



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