72 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



system for investigations dealing with the nature of the bacterial 

 chromatophore, 



A much simpler unit of photochemical activity has been shown to 

 be present in the green sulfur hsLCteriumChlorobiumthiosulfatophilu})! 

 (9), The cytoplasm appears granular and contains small (100 A) parti- 

 cles. After cell disruption, similar particles can be isolated and are 

 functional in carrying out photosynthetic phosphorylation. These parti- 

 cles have amolecularweightof about 1,500,000 and contain chlorophyll, 

 cytochromes, quinones, carotenoids, and lipids in amounts that seem 

 to indicate that this isolated structure may indeed represent the 

 minimal structural unit necessary for photosynthetic phosphorylation 

 (10,11). 



Thus, it now seems clear that there really are significant differ- 

 ences in the architecture of the photochemical apparatus of the various 

 photosynthetic bacteria. 



THE STRUCTURE OF THE GREEN SULFUR PHOTOSYNTHETIC 

 BACTERIUM CHLOROBIUM THIOSULFATOPHILUM STRAIN L 



As previously stated, Chlorobium appears to be an exception among 

 the photosynthetic organisms studied to date in that thin sections of 

 the cells observed by electron microscopy indicate the absence of any 

 form of visicular or lamellar structure known to be associated with a 

 photochemical apparatus. However, the authors have not yet made a 

 detailed analysis of the cell with electron microscopy. 2 



Following disruption of the cell, either by ultrasonic treatment or 

 with the Hughes press (which is not subject to the criticism of breaking 

 up internal membranes as is ultrasonic treatment), a sedimentable 

 fraction containing most of the pigment of the cell could be obtained. 

 Examination of the pellet by electron microscopy did not disclose any 

 vesicular or membrane associations, in agreement with our observa- 

 tions on cells of Chlorobium thiosiilfatophilum (strain L), 



These photochemical macromolecules behave differently from the 

 chromatophores obtained from other photosynthetic bacteria in several 

 ways. The pigments are more readily dissociated from them than from 

 the chromatophores of the purple bacteria and, indeed, the particles 

 appear to be perhaps the equivalent of subunits or chromatophore 

 fragments of a more highly organized system. Therefore, for this and 

 many other reasons, we prefer not to regard this pigmented component 

 of the cell as a chromatophore. Fig, 2 illustrates some of the physico- 

 chemical properties of this macromolecular system and the degree of 



2 Cohen-Bazire, in this volume, shows thin sections of other strains of Chloro- 

 hium which show ultrastructural differentiation which may or may not be as- 

 sociated with the pigment-bearing structure. 



