The binding of vanadate to the novel vanadium chloroperoxidase from C. inaequalis was investigated. Reconstitution experiments of apochloroperoxidase 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.
