The Photosynthetic Macromolecules of 



Chlorobium Thio sulfa tophilum^ 



J. A. Bergeron and R. C. FuLLER-f 



Biology Department, Brookhaven National Laboratory, 

 Upton, Xezc York, U.S.A. 



There is considerable modern evidence that in higher plants the entire 

 process of photosynthesis occurs in a microscopic but complex organelle — 

 the chloroplast (see review by Arnon [4]). The study of simpler systems 

 offers an advantage by eliminating variables which are not pertinent for 

 analysis of the basic light-dependent phenomena. This consideration 

 accounts, in large measure, for the current interest in bacterial photo- 

 synthesis. 



Knowledge of the submicroscopic basis of bacterial photosynthesis is 

 still fragmentary but is improving rapidly. It was assumed, until 1952, that 

 the photosynthetic pigments are bound to protein and dispersed through- 

 out the organism. At that time it was reported by Pardee et al. [33] that 

 the pigments sediment rapidly in crude extracts of the non-sulphur purple 

 bacterium, Rhodospirilhon ruhruni. The authors isolated the pigmented 

 component and applied the name chromatophore to it. The electron 

 micrographs of chromatophores which had been dried and shadowed with 

 metal revealed disks about iioo A in diameter. It was inferred that the 

 disks represented spheres with a diameter of about 600 A. This value 

 agreed roughly with the diameter of 400 A which had been calculated by 

 Stokes relation from the sedimentation coefficient (200 S) of the purified 

 preparation [35]. At the same time, similar electron micrographs also were 

 obtained by Thomas [38] with crude extracts of several photosynthetic 

 bacteria. These reports provided concrete evidence that the pigments are 

 localized in structures which are several orders of magnitude larger than 

 soluble proteins. 



The first evidence that this order of structural organization could be 

 associated with a relatively high degree of functional capability was pro- 

 vided in the report by Frenkel [19] of the light-dependent phosphorylation 

 of ADP by subcellular preparations of R. ruhriun. This report and the 



* Research carried out at Brookhaven National Laboratory under the auspices 

 of the U.S. Atomic Energy Commission. 



t Present address : Dartmouth Medical School, Hanover, Neiv Hampshire. 



