Protein composition of Rhodopseudomonas sphaeroides outer membrane

Abstract
The outer membrane polypeptide profile of R. sphaeroides was characterized. Solubilization of the outer membrane at 75 or 100.degree. C as opposed to room temperature resulted in the dissociation of 75-, 72- and 68-kilodalton (kdal) polypeptide aggregates into 29-, 26.5 and 21.5-kdal polypeptides, respectively, and a shared 47-kdal subunit. Similarly, an 88.5-kdal polypeptide dissociates into a 45-kdal monomeric form, and the electrophoretic mobility of a 58.5-kdal polypeptide was altered to 83 kdal. Lysozyme treatment of outer membrane fractions altered the 21.5-kdal polypeptide mobility to 23 kdal. The presence of lipid in both the 47-kdal polypeptide and an 8- to 10-kdal polypeptide was demonstrated by lipid staining and [14C]acetate incorporation. The lipid component of the 47-kdal polypeptide was neither lipopolysaccharide nor phospholipid. The 8- to 10-kdal polypeptide may be the equivalent of the Braun lipoprotein. Outer membrane fractions isolated from R. sphaeroides-specific phage RS1-resistant mutants were deficient in several of the high-MW aggregates involving the 47-kdal polypeptide.

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