High-resolution XANES studies on vanadium-containing haloperoxidase: pH-dependence and substrate binding.

High-resolution X-ray absorption vanadium K-edge spectra were recorded for samples of vanadium-containing bromoperoxidase from the brown alga, Ascophyllum nodosum, at pH 9, 7, 5 and 4, as well as for enzyme samples containing the substrates, hydrogen peroxide and bromide. The well-resolved features of the XANES spectra are discussed. The pH-dependence of the structure of the active site has been studied revealing no significant change of the absorption features. We were able to detect an interaction of H2O2 with the vanadium site of the bromoperoxidase using XAS spectroscopy, whereas addition of bromide causes no energy shift of the XANES spectrum. The possible role of vanadium during the enzymatic reaction is discussed on the basis of our results.