Formation of Glucuronic Acid during the Enzymic Hydrolysis of Conjugated Glucuronides

Abstract

β-Glucuronidase, an enzyme found in many animal tissues, catalyses the hydrolysis of conjugated glucuronides in vitro. The activity of preparations has been determined by measuring the increase in reducing power which occurs when they are incubated with glucuronides, the assumption being made that the substance causing reduction is glucuronic acid liberated during the hydrolysis^1–3. It has been suggested^4,5 that the synthesis of glucuronides in vivo proceeds by a reversal of the hydrolysis observed with this enzyme in vitro. Lipschitz and Beuding⁶ found, however, that the synthesis of glucuronides by liver slices is stimulated, not by glucuronic acid, but by certain C₃ compounds. By the method of Lohmar et al.⁷, the presence of d-glucuronic acid in the residue from hydrolysis of a glucuronide with β-glucuronidase has been demonstrated, suggesting that this enzyme is distinct from the system causing synthesis in Lipschitz and Beuding's experiments. A brief description of the experimental procedure follows. Fuller details will be published elsewhere.