Inhibition of rat intestinal and rat kidney mutarotase by actively transported sugars

Abstract

Properties of an enzyme isolated from rat intestine and rat kidney and which catalyzes mutarotation of sugars are described. Mutarotation of d-xylose, d-glucose, d-galactose, and l-arabinose was accelerated by the enzyme. Interaction of a number of sugars with the active site was examined by measuring inhibition of enzyme-catalyzed mutarotation of α-d-glucose. Based on this criterion, two sugars with no mutarotable hydroxyl (α-methylglucoside and 1-deoxyglucose) interacted strongly with the enzyme protein. Hexose sugars actively transported by intestine (d-glucose, d-galactose, 6-deoxy-d-galactose, α-methylglucoside, and 1-deoxy-d-glucose) inhibited the enzyme strongly. A number of hexoses and hexitols reportedly not actively transported (d-mannose, d-glucosamine, 2-deoxy-d-glucose, 2-deoxy-d-galactose, d-sorbitol, galactitol, and d-fructose) showed only alight inhibition. Pentoses with the same configuration at carbon 2 as d-glucose (l-arabinose and d-xylose) were good inhibitors of the enzyme; those differing at carbon 2 (d-lyxose and d-arabinose) were not. The enzyme possesses certain of the qualities of the hypothetical carrier or "permease" postulated for sugar transport. Possible significance of some inconsistencies with this hypothesis is discussed.