A study has been made of some of the properties of the inhibitors of
ß-glucuronidase in human urine. The inhibitory properties were determined by
comparing the effect on the activity of ß-glucuronidase 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-saccharolactone
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 he
separated from the conjugated estrogens in urine by gel-filtration on Sephadex. The
extent which non-substrate, competitive inhibitors or competitive substrates reduce
the activity of ß-glucuronidase is a function of the inhibitor constant (K(I)) or the
Michaelis constant (Km) respectively and the concentrations of these substances.
On prolonged standing the activity of ß-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.
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