Effects of glycosylation enzymes from membrane fractions, induced by chronic ethanol administration

To study the effect of chronic ethanol administration on the enzyme activities involved in the glycosylation processes (glycosidases and glycosyltransferases), we used 6-week ethanol-treated female Wistar rats and pair-control rats. Biological material was membrane fractions of microsomes and plasma membrane obtained by subcellular fractionation technique. Ethanol treatment increased with statistical significance the Vmax of N-acetyl-beta-D-glucosaminidase (P less than 0.10), beta-D-glucuronidase and alpha-D-mannosidase (P less than 0.001) activities from microsomal fractions and likewise it increased the Km value of beta-D-glucuronidase (P less than 0.001). In vitro doses of ethanol (0.1-1.7 M) were added to delucidate hypothetical membrane tolerance responses. However in vitro addition of ethanol provoked no differential effects in treated and untreated rats. Glycosyltransferase assays were carried out using [14C]sugar derivatives. We detected several glycosyltransferase activities in both microsome and plasma membrane fractions. Chronic ethanol exposure appeared to affect N-acetyl-neuraminyltransferase activity from both membrane fractions, producing a greatly increased incorporation in the presence of asialofetuin. Glucosyl and mannosyltransferase activities from plasma membrane fractions were also altered by ethanol treatment, producing an increased enzyme activity when reaction was performed in the presence of phosphatidylcholine + dolichol-phosphate liposomes.