Reactions of erythrocyte glycoproteins and their degradation products with various anti-I sera.

Three fractions of erythrocyte glycoproteins obtained from Sepharose 4-B chromatography were tested for I activity with ten serologically differentiated anti-I sera. The most active was fraction I, eluted at the void volume and containing the lowest amount of alkali-labile oligosaccharide chains. The desialization of glycoproteins increased their activity toward anti-I-s and anti-I-D sera, and did not change or decreased the activity toward anti-I-F sera. The most abundant fraction II (major sialoglycoprotein of erythrocyte membranes) showed no or only a very weak I activity, but I-active glycopeptides were isolated from products of digestion of fraction II with trypsin. The major product of digestion, sialoglycopeptide IIT-2 showed I activity only after alkaline elimination of alkali-labile oligosaccharide chains. The results indicate that I receptors are present in hindered form on apparently I-inactive components of erythrocyte membrane.