Studies on B-antigenic sites of human erythrocytes by use of coffee bean α-galactosidase

Treatment of human type B erythrocytes, erythrocyte membranes and membrane fractions with highly purified coffee bean α-galactosidase resulted in the disappearance of B activity and enhancement of H activity with concomitant release of galactose. In the case of B erythrocytes, enzyme treatment led to the release of 3.0 × 10⁶ molecules of galactose per cell, about 75% of which were found in the aqueous phase of butanol/water extracts of cell membranes. AB and O cells released 1.9 × 10⁶ and 0.8 × 10⁶ molecules per cell, respectively. All the galactose released from O cells came from glycolipid material lacking B activity. Application of a correction for the enzymically labile, non-B-active α-galactosides presumably also present in B cells would suggest that such B cells have approximately 2.2 × 10⁶ B-antigenic sites. No release of galactose was observed when membranes and cell fractions, prepared from B erythrocytes which had been previously incubated with α-galactosidase were treated with the enzyme, showing that all the α-galactosidase-labile galactose present in B-active macromolecules in intact red cells is located at sites available to the enzyme and can be readily removed. We did not find any significant differences in the number and distribution of the B-antigenic sites present in erythrocytes from secretors and from a nonsecretor B individual.