Formation of Blood-Group A Substance from H Substance by an α-N-Acetylgalactosaminyl Transferase

Abstract

An α-N-acetylgalactosaminyl transferase has been solubilized from hog gastric mucosal microsomes and purified approximately 14-fold by ion exchange chromatography. The enzyme catalyzes the transfer of tritum-labeled N-acetyl-d-galactosamine from UDP-[3H]acetylgalactosamine to blood-group H substance. The net synthesis of blood-group A substance was demonstrated using hemagglutination inhibition tests. The newly fromed blood-group A activity was shown to be susceptible to destruction by N-acetylgalactosaminidase from Helix pomatia. Part of the enzymatically synthesized radioactive blood-group A substance could be precipitated with human anti-A serum. The enzyme has a sharp pH optimum at pH 6.9 and requires Mn++ for maximum activity. The Km value for the glycosyl donor, UDP-acetylgalactosamine, is 33 μM.