BACTERIAL PHOTOSYNTHESIS 185 



present in components which are not free to exchange. These "fixed" 

 components— protein, phosphohpid, bacteriochlorophN'll, and the 

 carotenoids— are integral parts of the structure. Our data (Table 1) 

 for the chromatophore (Bergeron, 1958), if converted to a milligram 

 protein basis, agree very well with the data of Newton and Newton 

 ( 1957 ) for the fraction which they called the "small particles" 

 (chromatophores, see below). Since these authors reported that the 



TABLE 1 

 Chromatophore Composition 



Per Molecular Mole- Mole 



Substance Cent G/"Mole" Ch Weight cules Ch Ratio 



Carotenoid 1.5 2.0 X 10= 700 300 1 



Bacteriochlorophyll . . 4.2 5.5 X 10= 900 600 2 



Phospholipid 22.3 30 X 10= 900' 3000 10 



Protein 61.0 80 X 10= 120f/A.A. 67,000 A.A. 220 A.A. 



DNA — — — — 



PNA — — — — 



Other 11.0 12.5 x 10= — — — 



The per cent composition on a dry-weight basis has been converted to grams 

 per "mole" Ch by employing the "molecular weight" of thirteen miUion. By assigning 

 an average molecular weight to each substance, one can obtain an estimate of the 

 number of molecules of each substance in a chromatophore. The mole ratio repre- 

 sents a "minimal unit" of composition. This imit represents a molecular weight of 

 about 40,000. 



* Cephalin with Cm fatty acids. 



} Round value for average amino acid residue. 



phospholipid contains ethanolamine, phosphorus, and glycerol in a 

 1:1:1 ratio, we have treated the phospholipid as a cephalin. The 

 "molecular weight" of the chromatophore has been employed to 

 calculate the amount of each "fixed" substance in a "mole" of chro- 

 matophores. By assigning an average molecular weight to each 

 substance, one can estimate the numlDer of molecules of each type 

 in a chromatophore. By this method of calculation, the chromato- 

 phore contains 300 carotenoid molecules, 600 chlorophyll molecules, 

 3000 cephalin molecules, and protein equivalent to 67,000 amino 

 acids. The hypothetical "minimal unit of composition" (empirical 

 formula) is 1 carotenoid molecule, 2 bacteriochlorophyll molecules, 

 10 phospholipid molecules, and protein equivalent to 220 amino 

 acids. The "formula weight" is about 40,000. 



