Multiple components of blood group A and B antigens in human erythrocyte membranes and their difference between A1 and A2 status.

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Abstract
Human type O erythrocyte membranes were converted to type A1 by purified human A1-enzyme, to type A2 by purified human A2-enzyme, and to type B by purified human B-enzyme in the presence of radioactive sugar donors (i.e., UDP-N-acetylgalactosamine for A-enzyme and UDP-galactose for B-enzyme, respectively). Type A2 erythrocyte membranes were also converted to type A1 by purified A1-enzyme A1-enzyme. The labeled blood group antigens (A1, A2, and B) thus produced were analyzed by sodium dodecyl sulfate gel electrophoresis and by isoelectric focusing. It was demonstrated that blood group antigens on erythrocyte membranes are mostly (greater than 80%) glycolipid, not glycoprotein. The blood group glycolipids were presumably conjugated with other membrane materials and formed three major components in type A1 and type B erythrocyte membranes. However, two of the three components were absent in type O erythrocyte membranes converted to type A2. These results indicate the heterogeneity of blood group components in erythrocytes membranes and the qualitative difference between A1 and A2 antigens on these membranes.