Multiple kinetic forms of beta-glucuronidase.

Abstract

Partially purified chick embryo liver beta-glucuronidase and highly purified beta-glucuronidase from human placenta and rat preputial gland exhibit multiple kinetic forms which appear to exist in an equilibrium which can be shifted by varying the assay conditions. All three enzymes exist in a low Km form, which predominates at pH 3 and is stabilized by bovine serum albumin, and a high Km form, which predominates at pH 5.5 to 6.0 in the absence of serum albumin. At intermediate pH values both forms are present. Addition of 0.2 M NaCl shifts the equilibrium toward the high Km form. Both forms of these enzymes are active on 4-methyl umbelliferyl-beta-D-glucuronide and on the hexasaccharides of chondroitin-6-SO4, chondroitin, and hyaluronic acid, with the low Km forms showing 2- to 20-fold more activity on the oligosaccharide substrates than the high Km forms.