Polyacrylamide gel electrophoresis of the major proteincontaining fraction of Rhodopseudomonas spheroides chromatophores reveals the presence of five electrophoretic components. The predominant component has associated with it, nearly all of the chlorophyll and phospholipid initially present in the chromatophore. Because of its potential structural and functional importance, this fraction has been isolated and purified by sodium dodecyl sulfate (SDS) preparative acrylamide gel electrophoresis.

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... s isolated from preparative gels, this protein is at least 95% pure by virtue of the following criteria: protein chemistry, analytical gel electrophoresis, immunochemical reactivity, and a linear sedimentation-equilibrium plot. Chemical characterization of the protein-lipid-pigment complex reveals the presence of approximately 59% protein, 35% phospholipid, and 6% chlorophyll. Amino acid analysis of the purified protein shows a high content of nonpolar residues, no histidine or cysteine. Minimum molecular weights were estimated as 7,000 by amino acid analysis, 10,000 by SDS-acrylamide gel analysis, and 15,000 by sedimentation equilibrium analysis. Immunochemical characterization indicates that this protein is specific to only the photosynthetic membrane system derived from phototrophically grown cells.