The amino acid sequence of the Mc-specific major red cell membrane sialoglycoprotein--an intermediate of the blood group M- and N-active molecules.

The sequence and glycosylation of the N-terminal 12 amino acids of the blood group Mc-specific major erythrocyte (MN) membrane sialoglycoprotein was determined by analyses of aminoterminal tryptic and secondary V8 protease peptides from McM erythrocytes. As predicted previously, the sequence of the N-terminal seven residues was found to be: Ser-+Ser-+Thr-+Thr-Glu-Val-Ala-(+ = glycosylation). This suggests that the variant Mc represents the evolutionary link between the blood group M- and N-specific glycoproteins, which possess Ser or Leu and Gly or Glu at the positions one and five, respectively. The elucidation of the structure of the Mc-specific glycoprotein explains the specificity of various anti-M and anti-N reagents.