title: The structure of mixed cholesterol-phospholipid monolayers spread at the air-water interface as probed by interactions with band 3 protein from erythrocyte membranes.
abstract: Solubilized band 3 protein from human erythrocyte membranes (the anion transport protein) interacts strongly and specifically with monolayers of cholesterol spread at the air-water interface whereas, at pH 7-10, it shows only moderate interactions with phospholipid monolayers (Klappauf, E. and Schubert, D. (1979) Hoppe-Seyler's Z. Physiol. Chem. 360, 1225-1235). When band 3 protein, at pH 7 and an ionic strength of approx. 100 mM, is added to the subphase of mixed cholesterol-glycerophospholipid monolayers, the changes delta pi in monolayer surface pressure induced by the protein depend on the mole fraction X of sterol in the mixture. However, delta pi (X) only increases with increasing X towards the high values of delta pi that are characteristic of cholesterol monolayers if X greater than 0.67 +/- 0.04; at lower cholesterol content, delta pi (X) is practically identical to the value obtained with the pure glycerophospholipid. With mixtures of coprostanol and glycerophospholipids, the break in the delta pi (X) curves occurs when X = 0.33 +/- 0.03. Cholesterol-sphingomyelin and epicoprostanol-phosphatidylethanolamine mixtures show an increase of delta pi (X) when X greater than 0. The data seem to support earlier claims that cholesterol can form stoichiometric complexes with glycerophospholipids, the stoichiometries revealed by the band 3-monolayer interactions being 2:1 and 1:2. They also show that cholesterol-sphingomyelin complexes, if they should exist, must be structurally different from the cholesterol-glycerophospholipid complexes.
mesh_terms: D000388:Air; D001457:Anion Exchange Protein 1, Erythrocyte; D001798:Blood Proteins; D002784:Cholesterol; D004910:Erythrocyte Membrane; D006801:Humans; D007700:Kinetics; D008081:Liposomes; D010743:Phospholipids; D013261:Sterols; D014867:Water
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D001798:Blood Proteins; D008081:Liposomes; D010743:Phospholipids; D013261:Sterols; D014867:Water; D002784:Cholesterol