THE STRUCTURE OF THE PHOTOSYNTHETIC 



APPARATUS IN THE GREEN AND PURPLE 



SULFUR bacteria! 



R. C. FULLER, S. F. CONTI and D. B. MELLIN 



Department of Microbiology , Dartmouth Medical School 



Hanover, Neiv Hampshire 



INTRODUCTION 



The concept of the chromatophore as the basic structural unit of 

 bacterial photosynthesis has grown steadily since this structure was 

 first described by Schachman, Pardee, and Stanier (1) in 1952 and 

 subsequently shown to be functional in photosynthetic phosphorylation 

 by Frenkel (2). However, obvious exceptions to this rule have been 

 observed in recent years. Under most conditions of growth the cyto- 

 plasm of the photosynthetic bacterium Rhodomicrobium vannielii con- 

 tains a lamellar system which in all probability is the photosynthetic 

 apparatus of the cell (3). It also has been reported that lamellar 

 structures are characteristic of Rhodospirillum molischiamim (4,5) 

 and in some cases can be observed in R. rubrum. Recently Cohen- 

 Bazire and Kunisawa (6) have shown that in cells of R. rubrum grown 

 at high light intensity chromatophore synthesis is suppressed and that 

 the chromatophores, if present at all, are localized in the peripheral 

 areas of the cell. They suggest further that the photochemical apparatus 

 of this organism has its origin in the bacterial cytoplasmic membrane. 

 Boatman and Douglas have indications of similar relationships in 

 subaerobically grown cultures of R. rubrum (7). 



Electron microscopy of thin sections of cells of the purple bacterium 

 Chromatium strain D reveals the presence of circular vesicular 

 chromatophores throughout the cell. Disruption of the cells by various 

 means yields a preparation containing stable, uniform chromatophores 

 approximately 300 A in diameter, with a molecular weight of approxi- 

 mately 15,000,000; these are capable of catalyzing photosynthetic 

 phosphorylation without the addition of artificial electron transport 

 carriers (8), It has not been possible to obtain afunctional subunit 

 of this structure. This organism has therefore served well as a model 



1 This work was supported in part by the Charles F. Kettering Foundation; 

 Grant No. GB-76 from the National Science Foundation; and Contract No, AT 

 (30-1) 2801 from the U. S. Atomic Energy Commission, 



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