Interactions of band 3-protein from human erythrocyte membranes with phospholipid monolayers at the air-water interface.

Lipid monolayers at the air-water interface were used as a model system to study the interactions of solubilized band 3-protein of the human erythrocyte membrane with phospholipids. The changes in monolayer surface pressure accompanying protein incorporation were used as a measure of the strength of the protein-lipid interactions. The following results were obtained: (1) Both polar and apolar forces contribute to the protein-lipid interactions, the latter being predominant. (2) The interactions strongly depend on the pH of the monolayer subphase. They are much stronger at acid than at neutral or alkaline pH. (3) The influence of pH on the band 3-phospholipid interactions is mainly due to a pH-induced conformational change of the protein, the pK value of which is near 5.0. (4) At all pH values studied, band 3 shows the highest affinity for phosphatidic acid and phosphatidylglycerol, the lowest for sphingomyelin and phosphatidylcholine.