MEMBRANE-BOUND GLUCOSAMINE ACETYLTRANSFERASE IN COLEOPTILE SEGMENTS OF AVENA-SATIVA

The in vivo metabolism of D-[U-C-14]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-C-14]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.