Comparison of human MM, NN, and MN blood group antigens.

Types MM, NN, and MN blood group substances have been isolated. All three materials are glycoproteins containing about 24 % iV-acetyhreuraminic acid, 10 % galactosamine, 5% glucosamine, and 14% galactose. The hexosamines appear to be N-acetylated. Amino acid analysis of the glycoproteins reveals them to be similar in composition and to be especially rich in serine and threonine. Treatment of the types MM and NN glycoproteins with alkali resulted in a decrease of serine and threonine, suggesting that these two amino acids may be involved in linkage to the oligosaccharide moieties. The native glycoproteins seem to be more resistant to alkali cleavage of the carbohydrate-protein linkage than the sialic acid-free glycoproteins. All three of the glycoproteins seem to be equally susceptible to the action of neuraminidase.