Vanadium-containing peroxidases

Oxidation of sulfides catalyzed by haloperoxidases has been reviewed [74]. The natural biological role of haloperoxidases is to catalyze oxidation of chloride, bromide, or iodide by hydrogen peroxide. Three classes of haloperoxidases have been identified (i) those without a prosthetic group, found in bacteria, (ii) heme-containing peroxidases such as chloroperoxidase (CPO), and (iii) vanadium-containing peroxidases. 

A. Messerschmidt, X. Prade, and R. Wever, Implications for the catalytic mechanism of the vanadium-containing enzyme chloro-peroxidase from the fungus Curvularia inaequalis by X-ray structures of the native and peroxide form, Biol. Chem. 1997, 378, 309-315. 

Interestingly, unlike the heme-containing peroxidases myeloperoxidase and chloroperoxidase, the vanadium enzyme does not catalyze the direct disproportionation of H2O2 in the absence of bromide or iodide... 

Other vanadium-containing enzymes appear to be particularly important the production of polybrominated compounds in the sea (8, 70). The va-idium peroxidases utilize hydrogen peroxide to oxidize bromide or iodide, obably to corresponding hypohalite ions, which then react with NOM to oduce polyhalogenated compounds (eq 17) (8, 70). 

Messerschmidt A (1998) Metal Sites in Small Blue Copper Proteins, Blue Copper Oxidase and Vanadium-Containing Enzymes. 90 37-68 Meunier B, Bernadou J (2000) Active Iron-Oxo and Iron-Peroxo Species in Cytochromes P-450 and Peroxidases Oxo-Hydroxo Tautomerism with Water-Soluble Metal-loporphyrins. 97 1-36... 

Some haloperoxidases contain vanadium and a review of vanadium peroxidases has been given (Butler 1998). The structure of the vanadium enzyme in the terrestrial fungus Cur-vularia inaequalis has been determined by x-ray analysis (Messerschmidt et al. 1997), and the apochloroperoxidase possesses, in addition, phosphatase activity that can be rationalized on the basis of the isomorphism of phosphate and vanadate (Renirie et al. 2000). 

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

Most other peroxidases are Fe-heme-containing systems, which function as two-electron redox catalysts (Scheme 8). Dihydrogen peroxide oxidizes the Fe-heme moiety by two electrons, forming Compound 1 (a heme + FeIV=0 species) [97], Compound 1 oxidizes the halide ion, forming the active halogenating species. This mechanism cannot be operative in V-BrPO because the vanadium is already in its highest accessible oxidation state. Moreover, native V-BrPO does not oxidize bromide without an acceptable peroxide source. However, it should... 

Zinc deficiency places an increased demand on selenium (Se) pools in daphnids. As little as 5.0 p,g Se/L in zinc-free water eliminated overt cuticle damage and substantially increased reproduction, but did not alter the shortened life span. Cladocerans at the threshold of selenium deficiency will become overtly selenium-deficient when zinc supplies are lacking. Insufficient copper introduces cuticle problems in daphnids similar to those introduced by insufficient zinc or selenium, increasing the likelihood of a proposed relation between glutathione peroxidase (which contains selenium), and copper-zinc superoxide dismutase. High levels of dietary tin increased zinc loss from rats. Zinc prevented toxic effects of vanadium (lO.Omg/kg BW) on bone metabolism of weanling rats. 

---