Membrane‐bound glucosamine acetyltransferase in coleoptile segments of Avena sativa

Abstract

The in vivo metabolism of D‐[U‐14C]glucosamine and the in vitro properties of glucosamine acetyltransferase (EC 2.3.1.3), the first committed enzyme in the metabolism of exogenously supplied D‐glucosamine, were studied in coleoptile segments of Avena sativa L. cv. Sole II. D‐[U‐14C]glucosamine was taken up by oat coleoptile segments and sequentially metabolised to radioactive N‐acetylglucosamine, N‐acetylglucosamine 6‐P, N‐acetylglucosamine 1‐P, UDP‐N‐acetylglucosamine and UDP‐N‐acetylgalactosamine. In addition, N‐acetylglucosamine residues were incorporated into glycoproteins and glycolipids of the cells. All glucosamine acetyltransferase activity was found to be membrane‐bound. The enzyme was solubilized by either digitonin or CHAPS. The specificities and the kinetics of the membrane‐bound and soluble glucosamine acetyltransferase were determined. The effects of ions, nucleotides, nucleoside diphosphate amino sugars, coenzymes and group‐specific chemical probes on the rate of membrane‐bound and CHAPS‐solubilized enzyme were investigated. Our data indicate that UDP‐N‐acetylglucosamine and UDP‐N‐acetylgalactosamine do not exert a feed‐back control on the glucosamine acetyltransferase either in vivo or in vitro. Further, some nucleotides and the metal ions Cu2+, Zn2+, Fe2+, Fe3+ and Co2+ affect the activity of the enzyme in vitro.