Abstract
Jack bean urease was covalently immobilized on glutaraldehyde-pretreated chitosan membranes. Inhibition of the immobilized urease by boric acid was studied. The kinetic integration methods of: Walker and Schmidt, Jennings and Niemann, Booman and Niemann, Yun and Suelter, and Klesov and Berezin were used to determine kinetic constants of the urease-catalyzed urea hydrolysis in phosphate buffer pH 7.0, uninhibited and inhibited. Inhibition of chitosan-immobilized urease by boric acid was found to be competitive similar to that of the free enzyme, with the inhibition constant K i equal to 0.60 and 0.19 mM, respectively. The effectiveness of the inhibition was evaluated with the K M (int) K i ratio, which was determined to be close in value for both the ureases, 18.3 and 17.9, respectively. This proves that inhibitory potency of boric acid is comparable for both the enzymes. By relating K M (int) K i ratio to the electrostatic potential of chitosan, it was shown that boric acid acts as an inhibitor in its non-ionic form B(OH) 3, and not in the B(OH) 4 − form.
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