Some properties of the uridine diphosphate glucuronyltransferase activity synthesizing thio-beta-D-glucuronides.

1. Some properties of the UDP-glucuronyltransferase synthesizing thio-beta-d-glucuronides were investigated and compared with those of the enzyme synthesizing the O-glucuronides of analogous phenols. 2. Enzyme activity was generally similar for both classes of substrate in tissue distribution, intracellular location, optimum pH, perinatal development and induction by organ culture or by phenobarbital. 3. Certain differences were noted between the two types of activity in behaviour on storage and on activation, in kinetic behaviour and in distribution between Wistar and Gunn rats; the Gunn rats were not deficient in hepatic UDP-glucuronyltransferase activity towards o-aminothiophenol. 4. These differences are no greater than those exhibited in the synthesis of various O-glucuronides; therefore thiolic substrates could compete in vivo with phenolic compounds for access to the UDP-glucuronyltransferase complex as well as for UDP-glucuronic acid.