Since erythrocytes red blood cells do not hold any sub cellular organelles they are essentially a membranous sac for carrying haemoglobin their plasma membrane is a convenient model system for studies of membrane structure as it can readily be isolated from other membranes and intracellular elements. One of the major glycoprotein in the plasma membrane of erythrocytes is glycophorin A. amino acid protein a 131 that was the initial integral protein to be sequenced. This exposed in which the polypeptide chain of glycophorin having with the three domains:
1. An N-terminal region on the extracellular side of the membrane which having all the N- and O-linked glycosylation sites;
2. A hydrophobic central region which is buried in the hydrophobic core of the bilayer; and
3. A C-terminal region rich in polar and charged residues which is showing on the cytosolic side of the membrane.