Isolation and partial characterization of two minor glycoproteins from human erythrocyte membranes

Two minor glycoproteins GP-II and GP-III, were isolated from human erythrocyte membranes and characterized chemically and immunologically. The chemical composition of GP-II and GP-III was similar: GP-II consisted of 81% protein and 19 % carbohydrate of which 4.9 % was hexose. 5.4 % hexosamine and 7.8 % sialic acid. GP-III consisted of 76 % protein and 24 % carbohydrate of which 7.6 % was hexose, 7.2 % hexosamine and 8.1 % sialic acid. The amino acid composition of GP-II and GP-III was also similar. GP-II and GP-III, however, differed in chemical composition from the MN glycoprotein. GP-II and GP-III were associated with the blood group activities Ss, I and A, but not with the MN antigens. GP-III had higher blood group activities per μg of protein than did GP-II. The specific activities for the Ss blood group antigens were increased 3–10-fold by purification of GP-III from the aqueous phase of chloroform methanol extracts.