The subunits of Chlorobium limicola f. thiosu[fatophilum cytochrome c-553 and of Chromatium vinosum cytochrome c-552 have been obtained. Chlorobium cytochrome c-553 is split into the cytochrome and flavoprotein subunits by treatment with trichloroacetic acid; after the cytochrome is precipitated by l-2% trichloroacetic acid, the cytochrome subunit is extractable with buffer, while the flavoprotein subunit is not dissolved. The subunits of Chromatium cytochrome c-552 can not be obtained by the trichloroacetic acidtreatment. The flavoprotein subunit of the Chromatium cytochrome is obtained by isoelectric focusing in the presence of 6 M urea and 1% mercaptoethanol, while the cytochrome subunit is prepared by gel filtration in the presence of 6 M urea with Sephacryl S-200. Molecular weights of the cytochrome and flavoprotein subunits from the Chlorobium cytochrome are 11,000 and 47,000, respectively, while those of the two subunits from the Chromatium cytochrome are 21,000 and 46,000, respectively. The molecule of each flavocytochrome c is composed of one molecule of each of the cytochrome and flavoprotein subunits.
Physical and chemical measurements.
Spectrophotometric
determinations were performed in a Cary spectrophotometer model 16 using l-cm light path cuvettes.