The membrane location of the two B890-apoproteins from Rhodospirillum rubrum has been investigated by comparing the effects of mild proteolysis with proteinase K, and immunoprecipitation, with antibodies prepared against the B890-complex and its individual apoproteins, upon membrane vesicles. By using chromatophores (inside-out vesicles) and spheroplasts (right-side vesicles) both membrane surfaces have been interrogated. The N-terminal regions of both aproproteins are located at the cytoplasmic membrane surface, while the C-termini are most probably located at the periplasmic surface. The conformation of the N-terminal regions of the apoproteins is changed by the presence of carotenoid. In the carotenoid-containing strain S1, for example, the α-apoprotein is insensitive to digestion by proteinase K, while in the absence of the carotenoid in the mutant G9+six amino acids are removed from the N-terminus of the α-aproprotein by proteinase K treatment. © 1986.
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