Structure–Activity Studies of Glucose Transfer: Determination of the Spontaneous Rates of Hydrolysis of Uridine 5′-Diphospho-α- d-glucose (UDPG) and Uridine 5′-diphospho-α- d-glucuronic acid (UDPGA)

The pH-rate profiles for the hydrolysis of uridine 5′-diphospho-α- d-glucose (UDPG) and uridine 5′-diphospho-α- 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. From the measured pH-rate profiles for the hydrolysis of UDPG and UDPGA, the catalytic power ( k cat/ k uncat) of the glycosltransferases has been estimated for the first time to be in the order of 10 11–13.