Inhibition of 1-Aminocyclopropane-l-carboxylic Acid Synthase Activity by Polyamines, Their Related Compounds and Metabolites of S-adenosylmethionine

摘要

Basic amino acids, monoamines, diamines and polyamines inhibited the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase extracted from wounded mesocarp tissue of winter squash fruit (Cucurbita maximaDuch.). Among the amines tested, polyamines were highly effective, while the synthetic triamine, 1,8-diamino-4-aminomethyloctane, was an even stronger inhibitor than the polyamine spermine. Polyamines inhibited ACC synthase activity in a non-competitive manner, while metabolic inhibitors such as aminoethoxyvinylglycine and aminooxyacetic acid inhibited ACC synthase activity competitively, showing much lower Ki values than those of polyamines. ACC synthase activity was also inhibited by intermediates of the methionine-recycling pathway, 5′-methylthioadenosine andα-keto-γ-methylthiobutyric acid and by S-adenosylhomocysteine, a product of transmethylation of S-adenosylmethionine.It appears that polyamines not only inhibit ACC synthase activity but also suppress the induction of the enzyme. However, unlike previous reports, polyamines did not inhibit in vivo ethylene forming enzyme activity in the wounded mesocarp tis