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Abstract Crystalline cytochromes c2 (pI 6.2) and cc' (pI 5.6) have been isolated from extracts of Rhodospirillum rubrum with the aid of DEAE-cellulose chromatography. Analysis of the crude extract by the isoelectric focusing technique shows eight isoelectrically different forms of cytochrome c2, which ranged between pI 4.6 and 9.3, and seven different forms of cytochrome cc', which ranged between pI 4.1 and 9.3. The predominant forms amounted to more than 60% of each cytochrome and corresponded to the cytochromes finally purified. Two additional electron transfer proteins have been isolated in a homogeneous state from the R. rubrum extracts. One is an FMN-containing protein (pI 4.4, molecular weight = 140,000, Em,7 = -0.235 volt) with no detected dehydrogenase function. The other is cytochrome b557.5 (pI 4.6, mol wt = 450,000, Em,7 = - 0.204 volt) which does not react with carbon monoxide and is believed not to be related to the cytochrome o of R. rubrum cells.
Bartsch et al. (Thu,) studied this question.