PHOTOSYNTHETIC MACROMOLECULES OF CHLOROBIUM THIOSULFATOPHILIUM 323 



materials, such as the haemocyanins, which are classed as respiratory 

 proteins. Such considerations as these add interest to the study of the 

 photochemical activity and composition of this holochrome. 



Unequivocal evidence of photophosphorylation has not been obtained 

 with the isolated holochrome, but many reasons can be advanced to explain 

 failure. There is no indication, so far, in the composition data that this 

 particle is fundamentally different from the other photosynthetic systems. 

 There are two pigment types, the chlorophyll and the carotenoids. There 

 are enough chlorophyll molecules present [100] to meet the requirements 

 of the semiconductor hypothesis. The cytochromes, which figure promi- 

 nently in current concepts of the primary events [5, 27] are present albeit 

 in near-limiting quantities. It is not known, however, whether the import- 

 ant [10, 15] lipid-soluble quinone compounds are present. 



It seems reasonable to expect that continued study of this system will 

 help to define fundamental relationships between structure and function 

 in photosynthesis. 



Acknowledgments 



We wish to thank Dr. S. Conti and Aliss H. Kelly for culturing the 

 organisms employed in this study. The skilful technical assistance of 

 M. Gettner and W. Geisbusch is also gratefully acknowledged. 



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