Studies on β-glucuronidase. 2. The preparation and properties of three ox-spleen β-glucuronidase fractions

Abstract

Evidence was presented for the occurence in ox spleen of 3 beta-glucuroni-dase fractions having pH optima at 3.4, 4.5 and 5.2. An examination of the effects of the variation in substrate concn. upon reaction velocity, the energies of activation and the effects of various inhibitors, leads to the conclusion that the 3 fractions may be considered as separate enzymes. An analysis of the inhibition caused by excess substrate indicates that this inhibition is caused by the active enzyme-substrate complex combining with further molecules of substrate to form an inactive complex. It was shown, in confirmation of Oshima (1936), that various carboxylic acids inhibit beta-glucuronidase prepns. Of these citric acid inhibits the enzyme fractions with pH optima at 3.4 and 4.5 but has no action on the fraction with optimum at pH 5.2. Mucate and saccharate exert competitive inhibition on the enzyme fractions with pH optima at 3.4 and 4.5 but only non-competive inhibition on the fraction with optimum at pH 5.2. Suramin and heparin are inhibitors of beta-glucuronidase, the inhibition being pH-sensitive. The possible nature of the state of the separated enzymes in the original tissue is discussed, as also are the factors necessary for the inhibition of beta-glucuronidase.