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

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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.

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