Effect of ethanol on the in vitro sulfation of salivary mucin.

Abstract

In vitro sulfation of mucus glycoprotein by sulfotransferase from rat submandibular salivary gland and the effect of ethanol on this enzyme activity was investigated. Subcellular fractionation studies revealed that the enzyme which catalyzes the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to submandibular gland mucus glycoprotein is associated with Golgi-rich membrane fraction. The sulfotransferase enzyme exhibited optimum activity at pH 6.8 in the presence of 0.5% Triton X-100, 4 mM MgCl2, and 25 mM NaF. The enzyme was equally capable of sulfation of the desulfated intact as well as proteolytically degraded desulfated glycoprotein preparations, whereas the acceptor capacity of the intact mucus glycoprotein was 70% lower. The submandibular gland sulfotransferase activity was inhibited by ethanol. The rate of inhibition of mucus glycoprotein sulfation was proportional to the concentration of ethanol up to 0.4 M, at which concentration a 39% reduction in the sulfotransferase activity occurred. The apparent Km value of the enzyme for salivary mucus glycoprotein was 11.1 microM, and the Kl in the presence of ethanol was 0.93 M. The synthesized 35S-labeled glycoprotein gave on CsCl equilibrium density gradient centrifugation 35S-labeled peak which coincided with that of the glycoprotein. Alkaline borohydride treatment of this glycoprotein led to the liberation of the label into the acidic oligosaccharide alditol fraction. As the inhibition by ethanol of sulfotransferase enzyme occurred below its isosmotic concentration to plasma, the observed effect could also be detrimental to salivary mucus glycoprotein sulfation in vivo.