[Enzymatic investigations on the basis of the subgroups A1 and A2. (author's transl)]

Human O and A2 erythrocytes were incubated with the alpha-N-acetyl-galactosaminyltransferases isolated from the plasma of A1 and A2 individuals in the presence of labelled UDP-N-acetylgalactosamine. It could be shown that both O and A2 cells could be agglutinated by anti-A1 reagent when treated with the A2 transferase. Furthermore, the incorporated radioactivity was about equal for both cell types, corresponding to about 600.000 A sites newly formed; this number, however, is considerably higher than that found in native A2 cells (i.e. about 260.000). The results presented thus provide good evidence that the development of the subgroups A1 and A2 is based mainly on differences in enzyme kinetics of the A1 and A2 gene-dependent N-acetylgalactosaminyltransferases, rather than on variations in their substrate specificities.