322 J. A. BERGERON AND R. C. FULLER 



which can be extrapolated to the molecular level. An application of this 

 concept is illustrated in the model proposed for the ultrastructure of the 

 Chromatium chromatophore [6]. In this instance (Fig. 12), the submicro- 

 scopic architecture is generated by the juxtaposition of molecular units. 

 As in crystallization, it is the properties of the building block, a pigmented 

 protein with hydrophilic and hydrophobic poles, which determine the 



Fig. 12. Working hypothesis of the ultrastrvicture of the chromatophore. The 

 Chromatiimi chromatophore is described as a hollow sphere about 320 A in diameter 

 with a cortex about 90 A thick. The pigment molecules (B) aligned in a monolayer 

 are bounded internally by a phospholipid (A) monolayer and externally by a 

 60 A thick protein layer. The "minimal unit" of composition has been used as a 

 structural subunit. The protein has been folded and is related directly to two 

 chlorophyll molecules. On the average the protein is related indirectly to one 

 carotenoid molecule and ten phospholipid molecules. 



form of the assemblage. Such a scheme provides for specificity in a protein 

 of conventional dimensions, requires no assumptions beyond the principles 

 of molecular interaction for obtaining a higher level of organization, and 

 also allows for great flexibility in the composition of the lipid phase. 



If structural organization, above the molecular level, is a prerequisite 

 for photosynthesis, then the Chlorobiiim holochrome must approach the 

 limiting conditions. This particle is already within the physical range of 



