SOME OBSERVATIONS ON THE ORGANIZATION OF THE 



PHOTOS YN THE TIC APPARATUS IN PURPLE 



AND GREEN BACTERIA^ 



GERMAINE COHEN- BAZIRE 



Department of Bacteriology and Electron Microscope Laboratory , 

 University of California, Berkeley, California 



The light microscope does not have the resolving power necessary 

 to reveal the structure and organization of the photosynthetic apparatus 

 in cells of procaryotic organisms. Only one conclusion could be drawn 

 from the observations on photosynthetic bacteria and blue-green algae 

 by light microscopy: namely, that even the largest members of these 

 groups were devoid of organelles having the typical structure of chloro- 

 plasts. Our first positive information about the structure of the photo- 

 synthetic apparatus in these groups was accordingly derived from 

 physico-chemical studies on the pigment- bearing elements that could 

 be isolated from extracts of broken cells. As early as 1938, French 

 (1) showed that the native pigment complex can be extracted from 

 purple bacteria in water-soluble form and is bound to protein, as 

 shown by its precipitability with ammonium sulfate. In 1952, Schachman, 

 Pardee, and Stanier (2) demonstrated that the pigment complex in 

 extracts of R. rubrum prepared by mechanical abrasion or sonic 

 oscillation can be readily sedimented by high-speed centrifugation. By 

 applying a series of differential centrifugations, they succeeded in 

 isolating a physically homogeneous particulate fraction which had the 

 typical in vivo absorption spectrum of this bacterium. The particles 

 were isodiametric, and about 600 A in diameter. They were designated 

 as chromatophores. No fraction of corresponding size and uniformity 

 could be isolated from aerobically grown cells of /?. rubrum, which are 

 essentially devoid of photosynthetic pigments. 



Soon after, Frenkel (3) made the important discovery that chromato- 

 phores could perform photophosphorylation, and the investigation of 

 their biochemical properties was undertaken in several laboratories. 

 The finding that chromatophores possess significant photochemical 

 functions lent support to the belief that they are the structures re- 

 sponsible for the performance of photosynthesis in the bacterial cell. 



1 This work was supported by a grant from the National Science Foundation to 

 Professor Michael Doudoroff. 



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