Structure-activity studies of glucose transfer: determination of the spontaneous rates of hydrolysis of uridine 5'-diphospho-alpha-D-glucose (UDPG) and uridine 5'-diphospho-alpha-D-glucuronic acid (UDPGA).

The pH-rate profiles for the hydrolysis of uridine 5'-diphospho-alpha-D-glucose (UDPG) and uridine 5'-diphospho-alpha-D-glucuronic acid (UDPGA) in aqueous solution have been measured. The results obtained and a comparison with other data suggests that the mechanism of hydrolysis of each activated glycosyl-donor at pH 1-4 probably involves the slow ionisation, via an S(N)1 process, of the neutral molecule to a glycosyl ion and UDP. From these data, the catalytic power (k(cat)/k(uncat)) of the glycosyltransferases has been estimated for the first time to be in the order of 10(11-13).