Plant glycoprotein biosynthesis. Uridine diphosphate N-acetyl-glucosaminyltransferase from horseradish root.

A particulate enzyme preparation from horseradish root tissue was shown to catalyze the transfer of 2-acetamido-2-deoxy-D-[14C1]glucose from uridine diphosphate 2-acetamido-2-deoxy-D-[14C1]glucose to an exogenous acceptor molecule derived from horseradish peroxidase. The acceptor was produced from purified peroxidase by the action of a mixture of glycoside hydrolases covalently bound to Sepharose. The membrane preparation containing the transferase was purified approximately 12-fold by aqueous two phase distribution and by discontinuous sucrose density gradient centrifugation. Hydrolysis of the reaction product yielded glucosamine as the only radio-labeled substance. Precipitation of the reaction product by antiserum against peroxidase showed that the label was incorporated into peroxidase. The transferase utilized the acceptor most efficiently when only 12% of the 2-acetamido-2-deoxy-D-glucose was removed from the acceptor. The acceptor lost no accepting capabilities when heated to 100 degrees C for 3 min prior to assay. Trypsin treatment caused a 14% decrease in label incorporated while pronase treatment caused a 93% decrease,