The amino acids of M and N blood group glycopeptides are different

The major glycopeptides isolated from tryptic digests of M and N blood group glycoproteins of erythrocytes have different N-terminal amino acids, serine and leucine, respectively. They also differ elsewhere in that the blood group N glycopeptide has a glutamic acid residue in place of a glycine residue of the M glycopeptide, presumably at position 5 of both peptides.