A glucuronic-decomposing enzyme from rumen micro-organisms. 3. Mode of action, specificity and inhibition by acidic sugar derivatives

Abstract

A glucuronide-decomposing enzyme in sheep rumen was found to be a true beta-glucuronidase. Phenolphthalein and glucuronic acid were liberated in equivalent amounts by enzymic action on the conjugated glucosiduronic acid. Liberated glucuronic acid was identified by oxidation to D-glucosaccharic acid, from which derivatives were prepared. Rumen beta-glucuronidase is specific for beta-D-glucosidpyranuronic acids, and has no effect upon glycosides or on glycosiduronic acids of other sugars, nor upon methyl 4-0-methyl glucosiduronic acid. Acylglucuronides and dialyzable components of oxycellulose inhibit enzyme action upon phenolphthalein glucuronide. These compounds may be substrates for the enzyme. D-Glucosaccharo-1[forward arrow] 4-lactone is a strong competitive inhibitor of rumen beta-glucuronidase, although its affinity for this enzyme is lower than for tissue beta-glucuronidase. Boiled mucic acid preparations have no effect upon the rumen enzyme, in which respect the latter differs from tissue beta-glucuronidase.