Inhibition of jack bean urease by a mixture of boric acid and phosphate buffer pH 6.96

Inhibition of jack bean urease by a mixture of boric acid and phosphate buf fer pH 6.96 was studied. The inhibition constants of the mixture were deter mined in solutions of phosphate buffer (22-155 mM) by measuring the initial reaction rates for a series of boric acid concentrations (0-3 mM) at a ser ies of substrate concentrations (2-50 mM urea). It was found that boric aci d is a simple competitive inhibitor of urease with the inhibition constant of the system changing from 0.23 mM in 22 mM phosphate buffer to 0.76 mM in 155 mM phosphate buffer. It was shown, that boric acid and phosphate buffe r pH 6.96 are mutually exclusive competitive inhibitors of jack bean urease . The inhibition constants of boric acid and of phosphate buffer pH 6.96 in an inhibitor-free system were determined to be 0.12 mM and 21 mM, respecti vely.