The kinetics of hydrolysis of synthetic glucuronic esters and glucuronic ethers by bovine liver and Escherichia coli β-glucuronidase

1. The relative rates of hydrolysis of synthetically prepared β-d-glucuronic esters [aglycone: benzoic acid, veratroic (3,4-dimethoxybenzoic) acid, indol-3-ylacetic acid and ethylbutyric acid], and β-d-glucuronic ethers (aglycone: phenolphthalein, p-nitrophenol, 3,4-dimethoxyphenol, 3,4-dimethoxybenzyl alcohol) by commercial preparations of β-glucuronidase from bovine liver and Escherichia coli were investigated. The rates of hydrolysis of all compounds tested were followed by measuring the formation of glucuronic acid under conditions which do not affect the glycosidic ester bond. 2. The pH profiles of the substrates in reaction with the enzyme from both sources were determined, and substrate-saturation curves at the optimal pH for each substrate were constructed; double-reciprocal plots of activity against concentration were linear. 3. Comparison of kinetic data indicates that neither the type of sugar–aglycone linkage, nor the aglycone structure alone can explain the observed Km and Vmax. values. 4. α-d-Glucuronic esters of benzoic and veratroic acid resisted hydrolysis by β-glucuronidase from both sources.