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.