Methyl 3-amino-3-deoxy-beta-D-galactopyranosyl-(1-->4)-2-acetamido-2- deoxy-beta-D-glucopyranoside: an inhibitor of UDP-D-galactose: beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-D-glucose (1-->3)-alpha-D-galactopyranosyltransferase

UDP-D-galactose:beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-D- glucose alpha-(1-->3)-D-galactopyranosyltransferase [E.C. 2.4.1.151] transfers D-galactosyl-residues from the sugar nucleotide with retention of configuration. We report here that synthetic methyl 3'-amino-3'-deoxy-N-acetyllactosaminide (9), where the hydroxyl group normally undergoing galactosylation has been replaced by amino group, is an inhibitor for this enzyme with Ki = 104 microM. The mode of inhibition is not competitive, but appears to be specific, since other glycosyltransferases were not affected by 9.