COMPOSITION OF CHROMA TOPHORES 471 



TABLE 2. 



Chlorophyll -Carotenoid Ratios o/R. rubrum Cells Grown 

 Under Different Conditions (7) 



Electron donor Light intensity, ft.-c. 



Chlorophyll 

 Carotenoids 



Acetate 1100 1.62 



Succinate 1100 4.25 



Malate 860 3.90 



Malate 200 5.35 



Measurements on intact cells provide little information about the 

 variability of chromatophore composition and about possible means of 

 chromatophore replication. Although chromatophore material con- 

 stitutes as much as 40?c of the total cell protein, it is desirable to study 

 compositional variation with isolated cell fractions. Cohen- Bazire and 

 Kunisawa (8) made a start in this direction by isolating chromatophore 

 fractions by differential centrifugation in sucrose gradients and ex- 

 amining the chlorophyll-protein ratios in the isolated fractions derived 

 from cells undergoing rapid pigment synthesis. Table 3 contains some 

 of their results, which show that under these conditions the percentage 

 of cell protein in the chromatophore fraction does not change appre- 

 ciably even though the chlorophyll-protein ratio in the chromatophore 

 fraction is changing greatly. These data suggest that during pigment 



TABLE 3. 



specific Chlorophyll Contents ofR. rubrum Cells and Chron/atophores 

 During Induction of Pigment Synthesis (8) 



Hours growth Chlorophyll, //g/mg protein Total cell protein 



Extract Chromatophores ^^ ehromatophores,% 



1 1.55 3.28 47.3 



2 2.68 7.37 36.4 

 4 9 22.6 40 



6 11.8 31.5 37.5 



synthesis there is not de novo synthesis of the entire photosynthetic 

 apparatus, A similar conclusion is suggested by the finding that dark- 

 grown cells of Rhodospirilhim riibnim contain large amounts of anti- 

 genic material which cross- reacts serologically with specific chro- 

 matophore antibody (9). These data also suggest that studies of the 

 dark phosphorylation system mR. n-<5nn;? may ultimately aid in under- 



