Modification of Amino Groups of Human‐Erythrocyte Glycoproteins and the New Concept on the Structural Basis of M and N Blood‐Group Specificity

1 Various kinds of modification of amino groups of M and N blood group glycoproteins abolished their capacity to inhibit rabbit and human anti‐M and anti‐N sera. 2 The reversible modification of amino groups revealed that M and N blood group activity was restored after the removal of amino‐group‐blocking residues. 3 Modification of amino groups had an entirely different effect on the reactivity of red cell glycoproteins with Vicia graminea agglutinin. The serological activity of N glycoprotein towards Vicia graminea anti‐N agglutinin was unchanged, whereas the weak activity of M glycoprotein towards this anti‐N agglutinin was increased to the level of that of N glycoprotein. 4 These results indicate that there is a structural difference between M and N glycoproteins, which resides beyond the oligosaccharide chains. It suggests in turn that M and N blood group specificity is determined by amino acid sequence in the peptide chains of red cell glycoproteins.