Octapeptide segments from the amino terminus of glycophorin A contain the antigenic determinants of the M and N blood groups systems

: Human red blood cells with phenotype N/N and M/M were tested in an agglutination assay with anti-N and anti-M antibodies, respectively. After incubation of the synthesized octapeptide (Leu-Ser-Thr-Thr-Glu-Val-Ala-Met) from the N-amino terminus of glycophorin A, with anti-N antibody, there was significant inhibition of the agglutination of the N-positive cells. There was also inhibition of the agglutination of the M-positive cells with anti-M antibody by the synthesized octapeptide (Ser-Ser-Thr-Thr-Gly-Val-Ala-Met) from the M-amino terminus of glycophorin A. There was no inhibition, however, of the agglutination of M-positive cells with anti-M antibodies by the N-amino terminal octapeptide. Likewise, the M-amino terminal octapeptide did not inhibit agglutination of N-positive cells with anti-N. Because the synthesized octapeptides contained no carbohydrate, the anti-N and anti-M specificity appears to be determined principally by the peptides themselves. Further studies with the use of chimeric peptides indicate that the amino terminal amino acid leucine of N-glycophorin A is a primary determinant of the N antigen, whereas the amino terminal serine of M-glycophorin A is a primary determinant for the M antigen.