Inhibition of vanadium chloroperoxidase from the fungus Curvularia inaequalis by hydroxylamine, hydrazine and azide and inactivation by phosphate.

The first detailed inhibition study of recombinant vanadium chloroperoxidase (rVCPO) using hydroxylamine, hydrazine and azide has been carried out. Hydroxylamine inhibits rVCPO both competitively and uncompetitively. The competitive inhibition constant K(ic) and the uncompetitive inhibition constant K(iu) see are 40 and 80 microM, respectively. The kinetic data suggest that rVCPO may form a hydroxylamido complex, hydroxylamine also seems to react with the peroxovanadate complex during turnover. The kinetic data show that the type of inhibition for hydrazine and azide is uncompetitive with the uncompetitive inhibition constant K(iu) of 350 microM and 50 nM, respectively, showing that in particular azide is a very potent inhibitor of this enzyme. Substitution of vanadate in the active site by phosphate also leads to inactivation of vanadium chloroperoxidase. However, the presence of H(2)O(2) clearly prevents the inactivation of the enzyme by phosphate. This shows that pervanadate is bound much more strongly to the enzyme than vanadate.