MECHANISTIC STUDIES OF URIDINE-DIPHOSPHATE GLUCURONOSYLTRANSFERASE

Bisubstrate reaction kinetics and product inhibition studies were used to characterize the kinetic mechanism of a partially purified uridine diphosphate glucuronosyltransferase (UDPGT). These studies indicate t hat the reaction most likely occurs via a random order sequential mech anism. The effect of electron withdrawing and donating groups on the r ate of reaction was also determined. It was found that electron donati ng groups increased the rate of glucuronide conjugation. This result i s consistent with nucleophilic attack of the C-1 carbon of the UDP-glu curonic acid (UDPGA) by an S(N)2 mechanism. This is the first direct e vidence for a S(N)2 mechanism in UDPGT catalysis.