Urinary Inhibitors of ß-Glucuronidase

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Abstract
A study was made of some of the properties of the inhibitors of B-glucuronidase in human urine. The inhibitory properties were determined by comparing the effect on the activity of B-glucuro-nidase of urine pre-treated in many ways with that of a control containing no urine. A significant though variable fraction of the inhibition is caused by rapidly hydrolyzing competitive substrates of normal dietary or therapeutic origin. Other inhibitors such as 1,4-sac-charolactone probably account for a substantially greater fraction of the inhibition than do the competitive substrates. The inhibition by 1,4-saccharolactone is a function of the pH, temperature and time of equilibration of the medium. Saccharolactone can be separated from the conjugated estrogens in urine by gel-filtration on Sephadex. The extent to which non-substrate, competitive inhibitors or competitive substrates reduce the activity of B-glucuronidase is a function of the inhibitor constant (KI) or the Michaelis constant (Km) respectively and the concentrations of these substances. On prolonged standing the activity of B-glucuronidase is reduced more in the presence of urine than in the absence of urine. This phenomenon probably is due at least partially to the slow formation of saccharolactone from endogenous saccharic acid in urine.