PHOTOSYNTHETIC MACROMOLECULES OF CHLOROBIUM THIOsULFaTOPHILUM 



315 



parison of the absorption spectra of these zones with the original extract 

 reveals (Fig. 7) that the "yellow" zone is rich in carotenoids and deficient 

 in chlorophyll. The "green" zone, which accounts for the bulk of the 

 material, shows an appreciable decrease in the absorption due to caro- 

 tenoids. Two alternative explanations of this phenomenon are either that 

 a considerable fraction of the intracellular carotenoids are not incor- 

 porated into the pigmented particle or that these pigments are exposed and 

 tend to strip off during the progressive movement into more concentrated 



i I I I I I I I I I I I I I { 



200 



300 



400 



600 



700 



800 



900 



500 

 X m^ 



Fig. 7. Effect of centrifuging the crude extract in a linear gradient of sucrose 

 (io°o~5o"o). The pigmented particles are recovered in a "green" zone which is 

 followed by a " yellow " zone. By comparison with the original absorption spectrum, 

 the "yellow" zone is enriched in carotenoids and deficient in chlorophyll. The 

 "green" zone shows a decline in the absorption due to carotenoids and nucleic 

 acids. 



sucrose solutions. The latter alternative seems to be favoured by the 

 observation that these pigments are not left in the original layer but are 

 recovered in the sucrose gradient behind the green zone; then too, this 

 tendency is well defined only when gradients are employed. The spectra 

 also show disturbances in the 800 m/t maximum which are reminiscent of 

 the effect of carotenoids upon the infra-red absorption spectrimi in 

 Chroiuatium [i, 6, 8, 23, 24]. 



The components present in these extracts resemble in number and 

 sedimentation characteristics the extracts of non-photosynthetic bacteria. 

 In the photosvnthetic bacteria which have been investigated previously 

 \j,^^ the chromatophores have been present as a component in addition to 



