Enzymes vanadium

Krenn BE, Y Izumi, H Yamada, R Wever (1989) A comparison of different (vanadium) peroxidases the bro-moperoxidase of Corallina pilulifera is also a vanadium enzyme. Biochim Biophys Acta 998 63-68. 

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). 

The isolation of a vanadium nitrogenase suggests that vanadium may have a more important role in the nitrogen cycle than was recognized. This vanadium enzyme may have similarities with the chemical systems described in Section 33.3.8.1. 

Previously proposed mechanisms of the biosynthesis of certain chlorinated compounds have invoked electrophilic bromination of alkenes followed by passive chloride attack [62], Although this mechanism could explain the origin of adjacent brominated and chlorinated carbons, it does not readily account for compounds containing chlorine only. Thus, with the discovery of chloroperoxidase activity of the vanadium enzyme, the origin of specific chlorinated marine natural products can now be addressed. 

The two most important vanadium enzymes described to date are the vanadium nitrogenase (V—Nase) and haloperoxidase. 

On the basis of kinetic stndies the presence of a peroxo-intermediate was postdated and spectroscopic evidence for such an intermediate has been obtained. Brs", Br2, or HOBr appear to be the primary reaction prodncts of the enzyme-mediated peroxidation of bromide. The vanadium enzyme also nses phenylperacetic acid, m-chloroperoxybenzoic acid, and jo-nitroperoxybenzoic acid as oxidants, but alkyl peroxides such as ethylhydroperoxide, tert-butyl hydroperoxide, and cuminyl hydroperoxide are not substrates for the enzyme in the oxidation of bromide. The enzyme from the brown seaweed Ascophyllum nodosum does not display any specificity with regard to bromination of various organic nucleophilic acceptors which suggests a mechanism in which the oxidized bromine species are released into solution by the enzyme. Figure 1 gives a simple model for the reaction mechanism of the enzyme. 

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... 

Some of the vanadium enzymes are thermostable (19), although not as much as enzymes in thermophilic bacteria (40). For example, the enzyme from the red seaweed C. rubrum (22) is less stable than that from the brown seaweed A. nodosum. This may be related to the habitat of the seaweeds, since red seaweeds remain submerged even at low tide. In contrast, A. nodosum, which is found near the high-tide level, is dry most of the time and in summer is exposed to considerable heat. Similarly, the enzyme fromX. parietina, a lichen that grows on sun-exposed stones, has been reported to be thermostable (23). 

H. Vilter Isolation of the first vanadium enzyme, vanadate-depen-... 

Van Schijndel JWPM, Vollenbroek EGM and Wever R (1993) The chloroperoxidase from the fungus Curvularia inaequalis a novel vanadium enzyme. Biochim Biophys Acta 1161 249 - 256. 

M. Hawkins and J.R. Postgate, The alternative nitrogenase of AcotobactZK chKOOCOCCum is a vanadium enzyme. 

VANADIUM ENZYMES/MODELS Vanadate-Dependent Peroxidases... 

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