PHOTOOXIDATION AND PHOTOREDUCTION REACTIONS 



CATALYZED BY CHROMATOPHORES OF PURPLE 



PHOTOSYNTHETIC BACTERIA^^^ 



LEO P. VERNON 



Charles F. Kettering Research Laboratory, 



Yellow Springs, Ohio 



Photooxidation Reactions: 



Oxidation and reduction reactions are the essence of both plant 

 and bacterial photosynthesis. The photosynthesizing cell utilizes the 

 energy obtained from light to effect oxidation and reduction reactions 

 directed primarily toward control of the oxidation level of carbon 

 compounds and an associated production of ATP. It was early recog- 

 nized that under the influence of light, cells of the photosynthetic 

 bacteria had the ability to oxidize molecules of either inorganic sul- 

 phur or organic compounds and reduce carbon dioxide in a coupled 

 reaction (1). French demonstrated a photooxidation of ascorbic acid 

 by bacterial extracts of RJiodovibrio (2), and later Vernon and Kamen 

 reported a photooxidation of cytochrome c and DPIPH2^ by chromato- 

 phores of Rliodospirillum rubnim in the presence of air (3). Since 

 these reactions were performed aerobically, they were subject to the 

 criticism that the photooxidation could represent a nonbiological 

 oxidation catalyzed by the chlorophyll itself. Subsequently, however, 

 it was demonstrated that the reduced forms of DPIP, cytochrome c, 

 methylene blue, and indigo carmine were photooxidized by chromato- 

 phores of R. rubnim in the absence of oxygen if alternate electron 

 acceptors were added, such as fumarate (4), 



Lindstrom has extended the studies with DPIPH2 and has shown a 

 coupling of DPIPH2 photooxidation with the photo reduction of sulfate 



1 Contribution No. 107 from the Charles F. Kettering Research Laboratory. 



2 The term "chromatophore" is used in this presentation to mean thephotosyn- 

 thetlcally active particle or fragment which is obtained upon rupture of the 

 intact cell by sonic oscillation. There is some question concerning the origin 

 of these particles, but whether they exist as separate entities in the cell or 

 are part of the cell membrane does not significantly affect the conclusions 

 drawn from these experiments. 



3 In addition to the standard abbreviations, the following are used: TMPD, 

 N,N,N',N'-tetramethyI-p-phenylenediamine; MB, methylene blue; MBH2, re- 

 duced form of MB; PMA.phenylmercuric acetate; HQNO, 2-heptyl-4-hydroxy- 

 quinoline-N-oxide; DTNB, 5,5'-dithiobis (2-nitrobenzoic acid). 



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