| 93536 |
Schwaiger H, Tanner W: Effects of gibberellic acid and of tunicamycin on glycosyl-transferase activities and on alpha-amylase secretion in barley. Eur J Biochem. 1979 Dec 17;102(2):375-81.
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. |
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