Protein-induced conductivity changes in black lipid membranes and protein aggregation

Solubilized membrane proteins, especially the ‘integral’ ones, show a strong tendency towards aggregation. Little is known of the consequences this behaviour might have in experiments on protein-lipid interactions. Recently, however, it was briefly reported that protein association has an influence on lipid binding of apoprotein A-l from serum high-density lipoprotein. It may be anticipated that similar effects might also occur with membrane apoproteins. During the last several years, we have investigated the interactions of the ‘strongly bound’ protein fraction from human erythrocyte membranes with spherical and planar lipid bilayers. This protein fraction essentially consists of the two main integral proteins of the erythrocyte membrane: a protein of molecular weight 100 000 (‘band 3-protein’ and ‘glycophorin’, the membrane sialoglycoprotein; the band 3-protein being the dominating component. During our studies on the planar bilayers (black lipid membranes, BLM) we have found that the main peculiarity of the protein-BLM-system, the occurrence of large protein-induced changes in membrane conductivity, varies considerably with protein subfractions of different states of aggregation