184 MACROMOLECULAR COMPLEXES 



the observations on the minimum sokibihty and charge reversal of 

 crude extracts (Katz and Wassink, 1939; French, 1940). The pro- 

 nounced color of the chromatophores facilitates their identification 

 in the analytical ultracentrifuge. The color is related to only one 

 peak; thus the chromatophore preparation is monodisperse. The 

 sedimentation constant, measured at extreme dilution in de-ionized 

 water at neutrality, is 143 S corrected to 20° C. Since the chromato- 

 phore is not disrupted by lyophilization, it is possible to measure the 

 density of aqueous suspensions in terms of the gram fraction. The 



10 



GRAM FRACTION x 10 



20 



Fig. 4. The relation between the gram fraction and the density of aqueous 

 suspensions of lyophilized chromatophores. The equation of the line, Y = 0.9975 

 +0.199x, can be used to calculate the partial specific volume (v) and density 

 (D) of the chromatophore. 



resulting plot (Fig. 4) is Hnear and can be used to calculate the 

 partial specific volume (0.8 cc/g) at extreme dilution in pure water. 

 Since the chromatophores are spherical (see below), Stokes' relation 

 is applicable and an average particle diameter of 320 A is obtained. 

 The molecular weight is about thirteen million. 



Thus the chromatophore preparation contains the photosynthetic 

 pigments in a physiological relationship and is composed of a rather 

 uniform population of submicroscopic particles. 



Composition. The chemical composition of the chromatophore 

 is known reasonably well; about 89 per cent of the dry weight is 



