STRUCTURE OF PHOTOS YNTHE TIC SULFUR BACTERIA 75 



homogeneity of fractions after isolation and purification. With minimal 

 purification, the pigmented fraction shows a strong absorption maximum 

 at 260 m/2, indicating the presence of nucleic acids, but upon repeated 

 sedimentation and purification in buffered systems a single ultracentri- 

 fugal peak can be obtained. It is clear that the photochemical pigment 

 system is in an unaltered form and is free of both nucleic acids and 

 slower sedimenting components. The estimated molecular weight of 

 this particle from the above data is one and one-half million. This is 

 by far the simplest defined photochemical system described to date 

 which occurs in a natural state. 



Chemical analysis shows that the particulates isolated from 

 Chlorobium contain carotenoids, chlorophyll, cytochromes, quinones, 

 and phospholipids; the data of Hulcher and Conti (12), as shown in 

 Table 1, give a reasonable analysis of the particles. It is interesting 

 to note that the quinone associated with these particles is a new one 

 and very similar to plastoquinone (13). Olson and Romano (14) have 



TABLE 1 



Estinmtion of Cytochromes and Other Components in Chlorophyll -containing 

 Particles of Chromatium and Chlorobium 



Constituent 



Chromatium C. thiosidfatophilum 



myUmoles/1.0 ml suspension 



1 Protein determined by the spectrophotometric method of O. Warburg and W. 

 Chv\si\a.n,Biochem. Z., 310, 384 (1941). 



2 Calculated from total cytochrome, determined from extinction coefficients. 

 From Hulcher and Conti, Biochem. Biophys. Res. Commun., 3, 497 (1960). 



