PHOTOSYNTHETIC MACROMOLECULES OF CHLOROBIUM THIOSULFATOPHILUM 



319 



rods. This tendency of the macromolecules to organize into structures with 

 a higher degree of order than is observed in the organism is unusual. 



In the initial phase of this study, observations on the chemical composi- 

 tion of the pigmented fractions have dealt primarily with chlorophyll, 

 protein and nucleic acids. The spectrophotometric assay of chlorophyll 

 content is based on the specific absorption coefficient of this chlorophyll 

 in acetone [37] and a recent estimate of the molecular extinction coefficient 

 [14]. The quantitative relationship between the 723 m/x maximum in the 

 in vivo spectrum and the 652 m/z maximum of the chlorophyll in acetone 

 has been determined in order to allow direct measurement of chlorophyll 



0.400 



Q300 



0200 



O.IOO 



1 M I I M I I [ I I I I I I I i T I I M ; I 1 I i I ] M I I I I I M I 



-EXTRACTED IN HjS SATURATED 

 ACETONE, 652.0 m^ 



ON BEARER IN 0.1 M TRIS, 

 pH 78, 723.5 m^ 



M I I I I I M 



2.00 3.00 



CONCENTRATION 



4.00 



Fig. io. Quantitative determination of the relationship of the absorption at 

 652 ni/tt of the chlorophyll in H.^S-saturated acetone and the absorption at 723-5 

 m^ of the chlorophyll bound to the pigmented particle. 



content in the extract during fractionation (Figs. lo and ii). For the same 

 reason the nucleic acid and protein estimates have been limited to ultra- 

 violet absorption measurements. During the course of fractionation the 

 absorption maximum at 260 m^u decreases from an initial value w^hich is 

 two or three times greater than the chlorophyll maximum at 723 m/x to a 

 limiting value which is 13 of the chlorophyll absorption. The initial 280/ 

 260 m/i absorption ratio is about 0-5 and increases to 0-9; thus, the 50 S 

 fraction is quite free of nucleic acids. On a mass basis, the chlorophyll/ 

 protein ratio in the more highly purified preparations is 1/13. Assuming 

 that these two components account for the bulk of the mass of the particle, 

 this ratio represents about 100 chlorophyll molecules for each particle with 

 a molecular weight of 1-5 million. The cytochromes present in the 



