Enzymatic Conversion of Human Blood‐Group‐O Erythrocytes into A₂ and A₁ Cells by α‐<i>N</i>‐Acetyl‐<scp>d</scp>‐galactosaminyl Transferases of Blood‐Group‐A Individuals

Abstract

Human O‐erythrocytes, when incubated with UDP‐ N ‐acetyl‐ d ‐galactosamine and α‐ N ‐acetyl‐ d ‐galactosaminyl transferase prepared from gastric mucosa of blood‐group A 1 individuals, first acquired A 2 ‐specificity and, after continued incubation, became agglutinable by anti‐A 1 reagents. Group‐H specificity gradually disappeared. When A 2 ‐erythrocytes were subjected to the same treatment, they required a shorter time of incubation than O‐cells to develop A 1 ‐properties. These findings support the hypothesis of low and high densities of A‐specific sites on the cell surfaces of A 2 ‐ and A 1 ‐erythrocytes, respectively. Acetylgalactosaminyl transferase prepared from the gastric mucosa of blood‐group‐A 2 individuals was similar to the corresponding enzyme from A 1 ‐individuals in being capable of transferring acetylgalactosamine from UDP‐acetylgalactosamine to water‐soluble H‐substance and of converting O‐erythrocytes into A 2 ‐cells. With H‐substance as the substrate the blood‐group‐A 2 enzyme was considerably less active than the A 1 ‐enzyme based on equal weights of mucosal material extracted. When preparations of A 1 ‐enzyme were diluted so as to show a transferase activity towards blood‐group‐H substance equal to that of the A 2 ‐enzyme preparation, there was still a marked difference between the enzymes with regard to O‐erythrocytes, the speed of their conversion into A 2 ‐cells being much less with the blood‐group‐A 2 enzyme as compared with blood‐group‐A 1 enzyme. These experiments clearly indicate that blood‐group‐A 1 and A 2 enzymes have different substrate specificities.