78 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



of polymetaphosphate in discrete intracellular granules, from which 

 inorganic phosphate is released by an ADP- dependent and light- 

 independent reaction. The polymetaphosphate granules represent a 

 large proportion of the intracellular material. Fig. 3 illustrates the 

 effect of continued serial transfers on growing cultures of Chlorobium 

 in a phosphate deficient medium. It can be readily seen that the size 

 of the polymetaphosphate granules decreases with each transfer. Cells 

 essentially free of these polymetaphosphate granules were used to 

 study photosynthetic phosphorylation. 



The results shown in Fig. 4 indicate a rapid (and reproducible) rate 

 of photosynthetic phosphorylation over short periods of time. There 

 is still an indication of phosphate release which can mask the photo- 

 phosphorylation during longer periods of incubation. However, it now 

 seems clear that these functional macromolecules can catalyze the 

 light- dependent esterification of inorganic phosphate into ATP in the 

 absence of any artificial electron transport carriers. It is interesting 

 to note that Levine (15) recently has been able to demonstrate photo- 

 synthetic phosphorylation by Chlamydomonas chloroplasts for the first 

 time by growing cells deficient in polymetaphosphate. 



THE STRUCTURE OF THE PURPLE SULFUR 

 PHOTOSYNTHETIC BACTERLA. 



As stated previously, electron microscopy of thin sections of cells 

 of the purple bacterium Chromatiiim strain D has always revealed 

 the presence of circular vesicular chromatophores throughout the cell. 



Fig. 5 is a thin section of the bacterium indicating the classical 

 picture of the internal contents of the cell packed with spherical 

 chromatophores. 



The relationship of these chromatophores to the cytoplasmic mem- 

 brane in the photosynthetic bacteria has been a subject of speculation 

 for some time. In the succeeding article in this volume by Cohen- 

 Bazire, this discussion is extended in great detail in regard to the 

 nonsulfur photosynthetic bacterium R. ndrnim. It has been possible 

 to obtain a separation of the photosynthetic pigments and enzymatic 

 properties ordinarily associated with the bacterial cell membrane, 

 such as succinic dehydrogenase, in Chlorobium thiosuIfatopJiihn)! (IG). 

 However, such a separation has not been successfully achieved in the 

 purple bacteria. Recent experiments in our own laboratory in associa- 

 tion with Dr. R. Bennett have indicated that succinic dehydrogenase 

 activity is always associated with purified chromatophores, but can be 

 separated from the major fraction containing hexosamine which is a 

 constituent of the cell wall. Therefore, chromatophores appear bio- 

 chemically related to the cell membrane and not to the cell wall. 

 However, the difficulties involved in electron microscopy of such 



