Polypeptides of Human RBC Membrane

The red cell membrane consists of a lipid matrixes with which are associated membrane proteins. The membrane lipids are organized in a closely packed bilayer and show mobility. The proteins of the membrane can be classified into two main types, extrinsic and intrinsic proteins.

The extrinsic or peripheral proteins are readily dissociated from the membrane, and can be isolated by relatively simple means like manipulation of ionic strength or pH. They are believed to be associated with the polar heads of the lipid molecules. The polar amino acids are thought to be on the outer surface of the protein molecule and the non-polar acids in the interior.

The intrinsic or integral membrane proteins are tightly bound to the lipid bilayer. They dissociated from the membrane with difficulty, requiring more drastic treatment, such as the use of detergents. The intrinsic proteins are believed to have non-polar amino acid residues in the interior of the molecules as well as the surface of the molecule in contact with the membrane lipid. They thus have a higher percentage of non-polar amino acids. Some intrinsic proteins may partially penetrate either surface of the lipid bilayer, while others may span the entire membrane, protruding at both ends.