Studies on UDP-N-acetylglucosamine: α-mannoside β-N-acetylglucosaminyltransferase of rat liver and hepatomas

Abstract

When homogenates of rat liver and hepatomas were centrifuged at 78 000 × g, over 90% of liver N-acetylglucosaminyltransferase assayed with β-galactosidase- and β-N-acetylhexosaminidase-treated asialofetuin as acceptor was recovered in the particulate fraction, while as much as 24% of hepatoma transferase was in the supernatant fraction. The particulate transferase solubilized by 0.2% sodium deoxycholate emerged from a DEAE-cellulose column at 0.04 M NaCl (transferase A). The supernatant fractions from all the hepatomas tested contained a second N-acetylglucosaminyltransferase eluted from the column at 0.02 M NaCl (transferase B). Transferase B was absent from liver supernatant fraction. The activities of these transferases toward various acceptors and the effect of β-N-acetylhexosaminidase on their products suggest that both transferases are UDP-N-acetylglucosamine : α-mannoside β-N-acetylglucosaminyltransferase. Although ovalbumin and glycopeptide V, which was isolated from pronase digest of ovalbumin, were good acceptors, transferase A utilized ovalbumin and glycopeptide V with apparent K_m values of 0.44 and 0.33 mM, respectively, whereas the corresponding values for transferase B were 4.5 and 0.050 mM.