title: Effects of gibberellic acid and of tunicamycin on glycosyl-transferase activities and on alpha-amylase secretion in barley.
abstract: A crude membrane fraction was prepared from isolated aleurone layers, the secretory tissue of barley grains. The layers were pre-incubated in the presence or absence of the phytohormone gibberellic acid. The membranes catalyzed the transfer of [14C]mannose from GDP-[14C]mannose and of N-[14C]acetylglucosamine from UDP-N-[14C]acetylglucosamine to endogenous and exogenous dolichyl monophosphate. When gibberellic acid was present during the pretreatment the activity of the transferases was increased by a factor of two to three. A significantly increased activity was observable within four hours after the addition of gibberellic acid, whereas the gibberellic-acid-induced secretion of the glycoprotein alpha-amylase started only after 12 h. Tunicamycin inhibited the secretion of alpha-amylase by 60 to 80%. Intracellularly, however, no alpha-amylase was found to accumulate. On the other hand, tunicamycin did not inhibit the rate of total protein synthesis by more than 10%. The possibility is discussed that the synthesis of the protein portion of glycoproteins is specifically inhibited, when glycosylation is prevented.
mesh_terms: D000681:Amylases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D004287:Dolichol Monophosphate Mannose / Q000378:metabolism; D005875:Gibberellins / Q000494:pharmacology*; D005944:Glucosamine / Q000031:analogs & derivatives*; D006602:Hexosyltransferases / Q000378:metabolism*; D001467:Hordeum / Q000187:drug effects / Q000201:enzymology; D010944:Plants / Q000187:drug effects / Q000201:enzymology*; D014176:Protein Biosynthesis / Q000187:drug effects; D014415:Tunicamycin / Q000494:pharmacology*; D000516:alpha-Amylases / Q000378:metabolism*
chemical_list: D005875:Gibberellins; D014415:Tunicamycin; D004287:Dolichol Monophosphate Mannose; D006602:Hexosyltransferases; D000681:Amylases; D000516:alpha-Amylases; D005944:Glucosamine