Asymmetric binding of cytochrome to the membrane of human erythrocyte ghosts |
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Authors: | Kei-ichi Enomoto Ryo Sato |
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Institution: | Institute for Protein Research, Osaka University, Suita, Osaka 565, Japan |
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Abstract: | The intact, amphipatic form of cytochrome could bind to unsealed ghosts, but not to resealed ghosts, suggesting that the cytochrome could bind only to the inner (cytoplasmic) surface of the ghost membrane. This was further confirmed by the finding that the cytochrome could bind to closed, inside-out vesicles prepared from the ghosts. This asymmetric binding was not due to the exclusive localization of sialic acid and sugar chains on the outer surface of the ghosts membrane, because the cytochrome could not bind to ghosts even after enzymatic removal of these components. Although liposomes consisting of phosphatidylcholine or both phosphatidylcholine and sphingomyelin could effectively bind the cytochrome, this binding capacity was progressively decreased as increasing amount of cholesterol was included in the composition of phosphatidylcholine liposomes. Removal of cholesterol from resealed ghosts by incubation with egg phosphatidylcholine liposomes resulted in the binding of cytochrome to the outer surface of the treated ghosts. The possibility is discussed that the asymmetric binding is due to preferential localization of cholesterol in the outer leaflet of the lipid bilayer that constitutes the ghost membrane. |
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Keywords: | To whom correspondence should be addressed at: Institute for Protein Research Osaka University 5311 Yamada-kami Suita Osaka 565 Japan |
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