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

The in vivo metabolism of D-[U-C-14]glucosamine and the in vitro prope rties of glucosamine acetyltransferase (EC 2.3.1.3), the first committ ed enzyme in the metabolism of exogenously supplied D-glucosamine, wer e studied in coleoptile segments of Avena sativa L. cv. Sole II. D-[U- C-14]glucosamine was taken up by oat coleoptile segments and sequentia lly metabolised to radioactive N-acetylglucosamine, N-acetylglucosamin e 6-P, N-acetylglucosamine 1-P, UDP-N-acetylglucosamine and UDP-N-acet ylgalactosamine. In addition, N-acetylglucosamine residues were incorp orated into glycoproteins and glycolipids of the cells. All glucosamin e acetyltransferase activity was found to be membrane-bound. The enzym e was solubilized by either digitonin or CHAPS. The specificities and the kinetics of the membrane-bound and soluble glucosamine acetyltrans ferase were determined. The effects of ions, nucleotides, nucleoside d iphosphate amino sugars, coenzymes and group-specific chemical probes on the rate of membrane-bound and CHAPS-solubilized enzyme were invest igated. Our data indicate that UDP-N-acetylglucosamine and UDP-N-acety lgalactosamine do not exert a feed-back control on the glucosamine ace tyltransferase either in vivo or in vitro. Further, some nucleotides a nd the metal ions Cu2+, Zn2+, Fe2+, Fe3+ and Co2+ affect the activity of the enzyme in vitro.