UDP-N-acetylglucosamine-glycoprotein N-acetylglucosaminyltransferase in regenerating rat liver.

The assay condition for N-acetylglucosaminyltransferase activities in rat liver microsomal fraction was developed. The enzyme activities towards endogenous acceptors within 48 h after partial hepatectomy were lower than in controls, exceeding the control level by 96 h, and then higher than in controls up to 240 h after the operation. The changes in N-acetylglucosaminyltransferase activities towards exogenous acceptor (UDP-2-acetamido-2-deoxy-D-glucose: glycoprotein 2-acetamido-2-deoxy-D-glucosyltransferase, EC 2.4.1.51) were consistent with those in the enzyme activities towards endogenous acceptors at 144 h, but not at 48 h, after the operation. The contents of protein and the levels of protein-bound hexosamine in the liver microsomes were decreased at early period of liver regeneration. These results suggest that the acceptor capacity of liver microsomal proteins is diminished during first 48 h of the regeneration. This may be responsible for the decreased transfer of the amino sugar to nascent glycoproteins. However, the enzyme activity was enhanced at 144 h and the level of endogenous acceptors may increase.