Structure of the Ss Blood Group Antigens. I. Isolation of Ss-Active Glycopeptides and Differentiation of the Antigens by Modification of Methionine

Abstract

The Ss blood group antigen determinants were associated with the N-terminal tryptic and chymotryptic glycopeptides (residues 1-35 or 1-32) of the Ss sialoglycoprotein from human erythrocyte membranes. The N-terminal portion (residues 1-26) of these peptides is largely identical with that of the MN sialoglycoprotein. Ss activity of tryptic glycopeptides was higher than that of chymotryptic fragments, and the structural difference between the S and s antigens is located on the C-terminal part (residues 27-32) of these peptides. Chemical modification of sialoglycoproteins by various methods suggests that Glu residue(s) (positions 29 or 28, 31) and possibly .alpha.-GalNAc-Thr (residue 25) are recognized by anti-S and -s. Carboxymethylation, performic acid, H2O2 and cyanogen bromide treatment destroy the S antigen but have no effect on the s receptor. The S antigen is apparently determined by a methionyl-residue.