DISULFIDE PHO TOR EDUCTION 



309 



regenerates the disulfide and forms ATP. While this scheme is en- 

 tirely speculative, it is backed by work with other related systems 

 and chemical models (10-15). Our own work on inhibition of photo- 

 phosphorylation by disulfide exchange processes suggested that 

 coupling might take place through intervention of a sulfur- containing 

 species (16). 



It was the initial immunochemical work that led to a search for an 

 enzymatic system capable of photoreducing disulfides in the chroma- 

 tophores of Rhodospirillum nihnim (17). Some recent experiments 

 with this system have led to the view that the bacterial particles are 

 capable of undergoing light- induced conformational changes, and that 



Disulfide Photoreduction 



Time, Minutes 



Fig. 2. Photoreduction of the aromatic disulfide, DTNB, by 

 Rhodospirillum mbnim chromatophores. The reaction mixtures 

 contained in 3 ml. 0.2 M tris buffer, pH 7.5, 0.1 ml. chromato- 

 phores (O.D. 880 -■ 40), 20/imoles ascorbate, 0.1 ^mole dichloro- 

 phenolindophenol, 2 /ymoles methyl viologen, and 1 ^mole 5,5'- 

 dithiobis-2-nitrobenzoic acid (DTNB). Ionic strength {jj) was al- 

 tered by addition of (NH4)2SO^. Atmosphere, helium. 



