Bacitracin Inhibits the Synthesis of Lipid-linked Saccharides and Glycoproteins in Plants

The particulate enzyme fraction from mung bean (Phaseolus aureus) seedlings catalyzes the incorporation of mannose from GDP-[(14)C]mannose into mannosyl-phosphoryl-dolichol and of N-acetylglucosamine from UDP-[(3)H]N-acetylglucosamine into N-acetylglucosamine-pyrophosphoryl-polyisoprenol. Bacitracin inhibits the transfer of both of these sugars into the lipid-linked saccharides with 50% inhibition being observed at 5 mm bacitracin. This antibiotic did not inhibit the transfer of glucose from UDP-[(14)C]glucose into steryl glucosides or the incorporation of glucose into a cell wall glucan. Bacitracin also inhibited the in vivo incorporation of [(14)C]mannose into mannosyl-phosphoryl-dolichol and into glycoprotein by carrot (Daucus carota) slices. While bacitracin also inhibited the incorporation of lysine into proteins by these slices, protein synthesis was less sensitive than glycosylation. Thus at 2 mm bacitracin glycosylation was inhibited 92%, while protein synthesis was inhibited only 50%.