Human erythrocyte membrane contains two glycoproteins as major components. One is called glycophorin A, which is composed of 131 amino acids and 16 oligosaccharide chains. Glycophorin A is organized into three distinct domains on the basis of the clustering of the amino acids of similar type. These include (1) a glycosylated segment, (2) a hydrophobic segment, and (3) carboxyl terminal segment which has an unusual concentration of hydrophilic amino acids. This unique structure is consistent with the suggestions that glycophorin A has a transmembrane structure. Glycophorin A may functions to keep the cell free in blood stream while this assumption has not been supported by any conclusive results yet. Another major glycoprotein is called band 3 protein, which is supposed to function as anion transport channel. The structural analyses of this glycoprotein are under progress at a number of laboratories. The two major glycoproteins which are also the major intrinsic membrane proteins appear to make intramembrane particle in the membrane.
