BACTERIAL PHOTOSYNTHESIS 



187 



The Chromatophore as the Structural and Functional 

 Unit of Photophosphorylation 



Experiments with crude extracts of Chromatiwn by Williams 

 (1956) suggested that photophosphorylation might have occurred 

 as in the R. ruhrum preparations used by Frenkel (1954). Experi- 

 ments with the purified chromatophore fraction ( Fuller and Ander- 

 son, 1957, 1958) have unequivocally demonstrated the light-de- 

 pendent formation of ATP from ADP and inorganic phosphate. The 



Fig. 5. A plot of the rate of ATP formation against an index of chromato- 

 phore concentration. The proportionality which results indicates that photo- 

 phosphorylation does not depend upon interaction between chromatophores. 



reaction also requires Mg++ and is stimulated by small amounts of 

 the uncolored supernatant fluid. Two distinct factors are involved: 

 one is heat-labile, non-dialyzable, and can be precipitated by 35-45 

 per cent ammonium sulfate; the other is heat-stable, dialyzable, and 

 can be replaced by catalytic amounts of succinate or reduced diphos- 

 phopyridine nucleotide (DPNH). Photophosphorylation by Chro- 

 rnatium fractions has also been studied by Newton and Kamen 

 (1957). 



The rate of photophosphorylation by the purified chromatophores 

 is a linear function (Fig. 5) of the chromatophore concentration 

 (indirectly expressed by the bacteriochlorophyll content). A linear 

 dependence indicates that the chromatophores are not random frag- 

 ments of a photophosphorylating system; otherwise a falling rate 



