Composition and distribution of carbohydrate chains in glycoproteins of human erythrocyte membrane

The M-, N-, and MN-glycoproteins obtained from human erythrocytes by phenol-water extraction were purified by gel filtration and digested with Pronase and trypsin. The products of degradation were fractionated by gel filtration on Sephadex G-25 and DEAE-Sephadex A-50 and the fractions were examined by poly(acrylamide)-gel electrophoresis in the presence of dodecyl sodium sulfate, analyzed for carbohydrate and amino acid contents, and tested for M and N blood-group activity. From the results, it is suggested that the glycoprotein chains are composed of a hydrophobic moiety devoid of carbohydrate chains and a hydrophilic moiety containing carbohydrate chains of different compositions, irregularly distributed along the protein chains and linked to L-asparagine, L-serine, or L-threonine residues. The M and N activity typical for the undegraded glycoproteins, and the “basic” or “precursor-type” N activity, were found in different glycopeptide fractions.