The inhibition against arginase by NaF was studied by thermokinetic method at 37 ℃, pH＝7.4～9.4, 40 mmol?L^－1 sodium barbiturate-HCl buffer solution. As a result, this experiment indicate that the inhibitory effect of NaF towards arginase is a reversible non-competitive inhibition. For the same reaction, the inhibition rate depends only on pH value of solution, while substrate L-arginine and exogenous Mn^2＋ ion have no remarkable influence on the inhibition rate. The inhibition constants are 1.48 and 1.84 mmol?L^－1 under the condition of exogenous Mn^2＋ion concentration of 0 and 0.167 mmol?L^－1 respectively. It was suggested that the inhibitory effect do not result from the contest of fluorine anion and L-arginine for the active site of enzyme, and it could be due to that the fluorine anion was in place of (-OH₂ binding as a bridging ligand of the arginase double Mn(II) cluster. This effect obstructs the generation of hydroxyl anion that nucleophilically attacks the guanidino carbon of L-arginine and thus inhibits the reaction activity of arginase.

Key words: arginase, reversible non-competitive inhibition, NaF, thermokinetics