CYTOCHROME SPECTRA 



491 



500 600 



Wavelength (nop) 



Fig. 7. Rps. spheroides cytochrome 553 ferro-, , and ferri-, , 



absolute spectra (concentration and pH of cji;ochrome not stated) (5). Reproduced 

 by permission oi Biochimica et Biophysica Acta. 



in light-induced reactions (18) in the bacteria. The role of cytochro- 

 moid C is still unclear. 



Small differences are noted among the spectra of the three exam- 

 ples of cytochromoid C presented above, but the spectra clearly belong 

 to members of a single class of heme proteins. The doublet charac- 

 ter of the absorption bands is most apparent in the Soret band of re- 

 duced Rps. palustris cytochromoid C. Presumably small differences 

 in the immediate environment of the hemes in the several proteins 

 account for variations in the contribution of each heme to an absorption 

 peak, with consequent small shifts in extinction values and absorption 

 maxima. The affinity of R. rubruyn cytochromoid Cfor carbon monox- 

 ide is such that about 1.5 atmos, CO is needed for complete reaction 

 (19), The relatively higher CO-ferro- complex Soret extinction values 

 obtained with Rps. palustris and Chromatium cytochromoid C may 

 indicate that these heme proteins have greater affinity for CO than 

 does that of R. rubrmn. 



It has been suggested that cytochromoid C is identical with cyto- 

 chrome o (20), a bacterial oxidase which remains a spectroscopic 



