Vanadium Haloperoxidases

Abstract

This chapter describes the occurrence and the biological function of the vanadium bromoperoxidases and chloroperoxidases. These enzymes that contain vanadate as the prosthetic group catalyze the oxidation of halides to the corresponding hypohalous acids. Purification and molecular characterization of these enzymes is reported and a detailed comparison is made between a bromoperoxidase and a chloroperoxidase, both kinetically as well as structurally. The vanadate‐binding site in haloperoxidases shows an interesting homology with the binding site of phosphate in a large group of phosphatases. Finally, on the basis of mutagenesis studies, a catalytic mechanism is presented for the vanadium chloroperoxidase activity that details the role in catalysis of the amino acid residues in the first coordination sphere of the metal oxide.

Vanadium haloperoxidases: From the discovery 30 years ago to X-ray crystallographic and V K-edge absorption spectroscopic studies

“…After halide oxidation, the electron oxidized halogen intermediate "X + ", which is a mixture of different halogen species such as OX -, X 3 -or X 2 , may rapidly halogenate organic substrates in a non-enzymatic reaction (Scheme 1). In the absence of organic substrate, a second equivalent of H 2 O 2 is oxidized to form a single oxygen and X -[for reviews 1,7,8,10,44].…”

“…Haloperoxidases have been classified in two groups, according to the nature of their cofactor, vanadium or heme (iron-containing porphyrin) [1,[7][8][9][10]. Metal-free haloperoxidases have also been described in some bacteria [11].…”

Critical view on the monochlorodimedone assay utilized to detect haloperoxidase activity

“…Under standard reaction conditions an active protein could be purified, using the spectrophotometrical detection method as outlined in literature (Hager et Sundaramoorthy, 2001;Wever and Hemrika, 2001). Detailed analysis, however, made clear that the protein purified during this study was not linked to halogenation processes, neither in conjunction with MCD nor with potential ambigol-precursors.…”

“…The MCD-assay became the routinely used analytical method for identifying HPOs and for characterizing their halogenating activity (van Pee et al, 2006;Wever and Hemrika, 2001). In this enzymatically initiated reaction the actual halogenation is catalyzed unspecifically via free diffusible hypohalous acid and therefore, on substrates generally susceptible to halogenation, similar patterns of halogenation are observable as reported for non-enzymatic reactions with hypohalous acid in free solution.…”

“…Excreted by terrestrial fungi, their physiological function is rather discussed to be important for the degradation of plant cell walls. The produced hypohalorous acid facilitates penetration of the fungal hyphen into the host (Wever and Hemrika, 2001).…”