Membrane proteins of Rhodopseudomonas spheroides IV. Characterization of chromatophore proteins

Less than 5% of the protein isolated from Rhodopseudomonas spheroides chromatophores (designated Fraction P₁) is insoluble in 2-chloroethanol. Electrophoresis of these proteins on dodecyl sulphate-polyacrylamide gels reveals a gel pattern similar to those obtained from anaerobic and aerobic cell envelope proteins. Chromatophore P₁ is shown to be part of the chromatophore structure and its presence in the chromatophore is not due to contamination from the cytoplasmic membrane.Preparative dodecyl sulphate-polyacrylamide gel electrophoresis was performed to purify chromatophore P_ll proteins, which comprise 95% of the total chromatophore protein. These proteins contain approximately 60–65 mole% non-polar amino acids. Comparison studies of the amino acid compositions, tryptic and chymotryptic maps, molecular weights, and antigenic reactivity of chromatophore proteins demonstrate the existence of protein heterogeneity in chromatophores. These investigations lead us to suggest that chromatophore-specific proteins do not appear in other particulate or soluble fractions derived from either aerobic or anaerobic-grown cells.