470 APPENDIX 



TABLE 1. 



Gross Composition o/Chromatium Chromatophore Fractions (4) 



„ . Fraction sedimented at 

 Component 



25,000 X G 100,000 X G 



mg/mg protein 



Carbohydrate 0.410 0.116 



P-lipid 0.53 1.03 



Chlorophyll 0.020 0.040 



that chromatophore material was not readily separated from the large 

 amount of cell wall carbohydrate present in bacterial extracts. Fur- 

 thermore, the pigmented fractions always contained relatively large 

 amounts of phospholipid, which suggested a membranous origin. The 

 enrichment of phospholipid with pigment increase in derived fractions 

 and the simultaneous loss of polysaccharide from these fractions 

 suggest that the pigmented material, although attached to the cell 

 wall in some manner in the intact cell, can be divorced from it by 

 mechanical means on cell rupture (4,5), That the cell wall and cyto- 

 plasmic membrane of gram-negative bacteria, of which photosynthetic 

 bacteria are examples, are not readily separable has been known for 

 some time. Probably, purified chromatophore material will ultimately 

 be shown to contain little more than protein, pigment and phospholipid 

 as major constituents. The bacterial analog of starch formation in 

 chloroplasts appears to be synthesis of the cell wall polysaccharides 

 and slime layers; though glycogen deposits can be observed in the 

 bacterial cells, the deposits are not structurally associated with the 

 photosynthetic apparatus (6). 



Compositional Variation . 



The pigment composition of cells of photosynthetic bacteria can 

 vary extensively with growth conditions as was shown by Cohen- Bazire 

 et al. (1), Regulating factors are light intensity, aerobiosis and the 

 electron donor supplied for growth. A control point for this regulation 

 may be the redox level of a cellular respiratory carrier. The chloro- 

 phyll- carotenoid ratio of the cells can also be varied although the two 

 pigment classes respond as a group to similar factors (Table 2). This 

 response indicates no rigid control over the introduction of the pig- 

 ments into chromatophore material as a stoichiometric combination. 

 Furthermore, chromatophore formation does not require simultaneous 

 introduction into the structure of colored carotenoids, as indicated by 

 work with carotenoidless mutants, which yield photosynthetically active 

 chromatophore material containing chlorophyll but devoid of caro- 

 tenoids. 



