Analysis of galactosyltransferase activity in rat gastric mucosa using crude mucosal homogenate

Mucus glycoprotein is one of the major components of gastric mucus which plays an important role in mucosal defensive mechanisms as a mucus-bicarbonate barrier. Analysis of the mucus glycoprotein synthesis is a useful tool for evaluating gastric mucosal defensive factors. UDP-galactosyltransferase (UDP-Gal-T) is one of the regulating enzymes for the synthesis of the mucus glycoprotein. In the present paper, we studied assay methods for UDP-Gal-T activity in rat gastric mucosa using radiolabeled UDP-galactose and two different kinds of acceptor proteins, namely ovomucoid and asialomucin, and analyzed effects of antisecretory agents on the UDP-Gal-T activity. We used crude supernatants of homogenized scrapings of the fundic part of rat stomach as an enzyme preparation and determined optimal conditions. In each acceptor, Mn2+ and the non-ionic detergent Triton X-100 were required for the enzyme activity. With each acceptor molecule, the type of glycosidic linkages of galactose was beta-type linkage. With asialomucin as an acceptor, UDP-Gal-T activities of rat gastric mucosa decreased after intraperitoneal administration of antisecretory agents, while change of the enzyme activity was not observed with ovomucoid as an acceptor.