Blood-Group-ABH Antigens of Human Erythrocytes. Quantitative Studies on the Distribution of H Antigenic Sites among Different Classes of Membrane Components

The contribution of blood-group-active glycolipids and glycoproteins to the blood-group-ABH character of human erythrocytes was investigated. For that purpose the blood-group-H sites of human O cells were converted in vitro into group-A sites by transfer of alpha-N-acetyl-D-[14C]galactosamine residues with the aid of the blood-group-A gene-dependent alpha-N-acetylgalactosaminyl transferase prepared from human A1 plasma. Upon partition of the red cell membranes between water and organic solvent, about 5% of the label was found in the organic phase and about 20% in the water phase, thus reflecting the distribution of blood-group antigenic sites between glycosphingolipids with short carbohydrate chains and polyglycosylceramides, respectively. The fact that about 70% of the radioactivity remained tightly bound to the membranes and could only be released by treatment with pronase provided good evidence that the bulk of blood-group-H determinants is bound to glycoprotein material. Following these results it can thus be assumed that blood-group-ABH activity of human erythrocytes is determined preferentially by group-specific glycoproteins rather than glycolipids.