The vanadium chloroperoxidase from the fungus, Curvularia inaequalis. Evidence for the involvement of a histidine residue in the binding of vanadate.

The binding of vanadate to the novel vanadium chloroperoxidase from C. inaequalis was investigated. Reconstitution experiments of apo-chloroperoxidase by vanadate at different pH values showed that in the pH 6-7 range an acid/base group is present which affects the binding of the vanadate. It is proposed that this group is a histidine. This hypothesis was tested by specifically modifying this residue using diethylpyrocarbonate. In the apo-enzyme 9 histidines were modified, whereas in the holo-enzyme 6 histidines were modified. Modification with diethylpyrocarbonate had no effect on the chlorinating activity of the holo-enzyme, but when the apo-enzyme was modified the reactivation by vanadate was strongly inhibited. We conclude that histidine in the active site of chloroperoxidase is involved in the binding of vanadate.