Separation into two major forms of beta(1-3)N-acetylglucosaminyltransferase from human serum

The major beta(1-3)N-acetylglucosaminyltransferase [beta(1-3)GlcNAc-transferase] activity in human serum was isolated by DEAE- and CM-Sepharose column chromatography. This enzyme fraction consisted of two forms of the enzyme, which were separated from each other on a DEAE-Sepharose column and designated as GNAc-TI and GNAc-TII, respectively. They have the same molecular weights (about 90,000), optimum pH values (between pH 7.5 and 8.5) and apparent Km values for N-acetyllactosamine and lactose (7.1-8.8 mM and 10.9-11.5 mM, respectively). Glycosidase and methylation analyses of the reaction products demonstrated that both the enzyme catalyze exclusively the transfer of one N-acetylglucosamine to position C-3 of the terminal galactose of lactose in the beta linkage.