Vanadium-Dependent Haloperoxidases

In vanadium-dependent haloperoxidases, the metal center is coordinated to the imidazole system of a histidine residue, which is similarly responsible for creating hypochlorite or hypobromite as electrophilic halogenating species [274]. Remarkably, a representative of this enzyme class is capable of performing stereoselective incorporation of halides, as has been reported for the conversion of nerolidol to various snyderols. The overall reaction commences through a bromonium intermediate, which cyclizes in an intramolecular process the resulting carbocation can ultimately be trapped upon elimination to three snyderols (Scheme 9.37) [275]. 

An empirical method for correlating the oxidation state of a metal ion with the coordination geometry and the bond lengths Bond valence sum analysis has been used in characterizing the structural features of vanadium-dependent haloperoxidases . ... 

Enzymes requiring vanadium for catalytic activity. Perhaps the best studied of these are the vanadium-dependent nitrogenases [EC 1.18.6.1]. Other vanadium-dependent enzymes include vanadium haloperoxidase, vanadium chloroperoxidase, and vanadium bromoper-oxidase. In the vanadium chloroperoxidase and bromo-peroxidase reactions, the vanadium(V) is coordinated in a trigonal bipyramidal site to a histidyl residue, three nonprotein oxygens, and, presumably, to a hydroxide. 

Weyand M, Hecht H-J, KieP M, Liaud M-F, Vilter H, Schomburg D (1999) X-ray Structure Determination of a Vanadium-dependent Haloperoxidase from Ascophyllum nodosum at 2.0 A Resolution. J Mol Biol 293 595... 

Almeida M, Humanes M, Melo R, Silva JA, Frausto da Silva JJR, Vilter H, Wever R. (1998) Saccorhiza polyschides (Phaeophyceae Phyllariaceae) a New Source for Vanadium-Dependent Haloperoxidases. Phytochemistry 48 229... 

Figure 9.6 Proposed mechanism of vanadium-dependent haloperoxidases.

Conte, V., O. Bortolini, M. Carraro, and S. Moro. 2000. Models for the active site of vanadium-dependent haloperoxidases Insight into the solution structure of peroxo-vanadium compounds. J. Inorg. Biochem. 80 41 -9. 

Many peroxovanadates have potent insulin-mimetic properties [1,2]. Apparently, this functionality derives from the ability of these compounds to rapidly oxidize the active site thiols found in the group of protein tyrosine phosphatases that are involved in regulating the insulin receptor function [3], The discovery of vanadium-dependent haloperoxidases in marine algae and terrestrial lichens provided an additional stimulus in research toward obtaining functional models of peroxidase activity, and there is great interest in duplicating the function of these enzymes (see Section 10.4.2). 

The haloperoxidases are a class of enzymes that catalyze the oxidation of halides via a reactive peroxometal active site. These enzymes are named according to the most electronegative halide they are able to oxidize. Hence, a bromoperoxidase can oxidize bromide and iodide but not chloride, whereas a chloroperoxidase can oxidize all three. Haloperoxidases are found in most living organisms and predominately fall into two classes the iron heme-based and vanadium-dependent enzymes. Of these, heme-based enzymes are found in mammals, where they provide a vital... 

Zampella, G., J.Y. Kravitz, C.E. Webster, P. Fantucci, M.B. Hall, H.A. Carlson, V.L. Pecoraro, and L. de Gioia. 2004. Quantum mechanical models of the resting state of the vanadium-dependent haloperoxidase. Inorg. Chem. 43 4127-4136. 

This book does not follow a chronological sequence but rather builds up in a hierarchy of complexity. Some basic principles of 51V NMR spectroscopy are discussed this is followed by a description of the self-condensation reactions of vanadate itself. The reactions with simple monodentate ligands are then described, and this proceeds to more complicated systems such as diols, -hydroxy acids, amino acids, peptides, and so on. Aspects of this sequence are later revisited but with interest now directed toward the influence of ligand electronic properties on coordination and reactivity. The influences of ligands, particularly those of hydrogen peroxide and hydroxyl amine, on heteroligand reactivity are compared and contrasted. There is a brief discussion of the vanadium-dependent haloperoxidases and model systems. There is also some discussion of vanadium in the environment and of some technological applications. Because vanadium pollution is inextricably linked to vanadium(V) chemistry, some discussion of vanadium as a pollutant is provided. This book provides only a very brief discussion of vanadium oxidation states other than V(V) and also does not discuss vanadium redox activity, except in a peripheral manner where required. It does, however, briefly cover the catalytic reactions of peroxovanadates and haloperoxidases model compounds. 

Almeida, M., M. Humanes, R. Melo, J.A.Silva, J.J.R. F da Silva, H. Vilter, and R. Weaver. 1998. Sacchorhiza polyschides (Phaeophycea Phyllariacea) a new source for vanadium-dependent haloperoxidases. Phytochem. 48 229-239. 

Another vanadium-dependent haloperoxidase from the marine alga Corallina officinalis was shown to possess a matching opposite enantiopreference by forming (5)-sulfoxides [1343, 1344]. Although simple open-chain thioethers were not well transformed, cyclic analogs bearing a carboxylic acid moiety in a suitable position within the substrate were ideal candidates [1345]. 

SF2415B1 in a nonstereoselective fashion. This has opened up possible experimental approaches to understanding the absence of selectivity in other vanadium-dependent halo-peroxidases and identifying potentially stereoselective haloperoxidases from sequence data. 

For electron-rich substrates, nature often uses flavin-dependent halogenases (e.g. chlorotetracycline), vanadium haloperoxidases (snyderol, Figure 7.4) or heme-iron haloperoxidases (tetraiodothyronine. Figure 7.4) for this role (Figure 7.5). For electron-deficient molecules such as alkanes, mononuclear iron... 

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