Haloperoxidases

These are of primary signihcance in the biosynthesis of organohalogen compounds (Neilson 2003), which are distributed among mammals, marine biota, bacteria, and fungi. 

Chloroperoxidase activity has also beeu fouud amoug degradative euzymes  

Au iuducible euzyme iu the hacttimvaRhodococcus erythropolis NI86/21 that is iuvolved iu the degradatiou of thiocarbamate herbicides is a uouheme haloperoxidase, which does uot occur iu other straius of rhodococci that cau degrade thiocarbamates (de Schrijver etal. 1997). 

Type of Enzyme Group Organism Halogen Reference 

Heme Bacterium Streptomyces phaeochromogenes Br van Pee and lingens (1985a) 

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Some of the major enzyme groups that facilitate this transformation are heme-containing MOs of the cytochrome P450 type [111], alkane hydroxylases, xylene monooxygenases, styrene monooxygenases [105], and haloperoxidases [112],... 

Enzyme-mediated chiral sulfoxidation has been reviewed comprehensively in historical context [188-191]. The biotransformation can be mediated by cytochrome P-450 and flavin-dependent MOs, peroxidases, and haloperoxidases. Owing to limited stability and troublesome protein isolation, a majority of biotransformations were reported using whole-cells or crude preparations. In particular, fungi have been identified as valuable sources of such biocatalysts and the catalytic entities have not been fully identified in all cases. 

Heme-dependent haloperoxidases generate HOX as reactive species from H2O2 and X, which represents an X+ equivalent capable of undergoing electrophilic addition at electron-rich centers [270,271]. Aprototype biocatalyst of this group is the chloroperoxidase from Caldariomyces Jumago [272]. In many natural systems, such enzymes are responsible for the halogenation of electron-rich aromatic cores. 

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]. 

Kataoka M, K Honda, S Shimizu (2000) 3,4-Dihydrocoumarin hydrolase with haloperoxidase activity from Acinetobacter calcoaceticus. Eur J Biochem 267 3-10. 

Pelletier I, J Altenbuchner (1995) A bacterial esterase is homologous with non-haem haloperoxidases and displays brominating activity. Microbiology (UK) 141 459-468. 

Picard M, J Gross, E Liibbert, S Tolzer, S Krauss, K-H van Pee (1997) Metal-free haloperoxidases as unusual hydrolases activation of HjOj by the formation of peracetic acid. Angew Chem Int Ed 36 1196-1199. 

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). 

In addition to these mechanisms, the degradation of thiocarbamates may be carried out in Rhodococcus erythropolis NI86/21 by a herbicide-inducible nonheme haloperoxidase (de Schrijver et al. 1997). 

Van Pee, K.-H., Dong, C., Flecks, S. etal. (2006) Biological halogenation has moved far beyond haloperoxidases. Advances in Applied Microbiology, 59, 127-157. 

Many marine organisms have enzymes called haloperoxidases that convert nucleophilic iodide, bromide, or chloride anions into electrophilic species that react like I+, Br+ or Cl+. 

Thus a number of enzymes have been shown to be able to control the oxidation of sulfides to optically active sulfoxides most extensive investigations have concentrated on mono-oxygenases (e.g. from Acinetobacter sp., Pseudomonas putida) and haloperoxidases1 071 (from Caldariomyces fumago and Coral I ina officinalis). A comparison of the methodologies11081 led to the conclusion that the haloperoxidase method was more convenient since the catalysts are more readily available (from enzyme suppliers), the oxidant (H2O2) is cheap and no cofactor recycling is necessary with the haloperoxidases. Typical examples of haloperoxidase-catalysed reactions are described in Scheme 24. 

Vanadium is known to be essential, and is a constituent of some haloperoxidases as well as nitrogenases in some nitrogen-fixing organisms. It is particularly abundant in tunicates (a species of marine organisms) and in Amanita toadstools. 

It is also of interest to point out that the amino acid sequence and structure of the active site of vanadium haloperoxidases is conserved within several families of phosphatases, with conservation of the amino acids involved in vanadate binding in one and phosphate binding in the other. 

Kupper FC, Schweigert N, Ar Gall E, Legendre J-M, Vilter H, Kloareg B (1998) Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide. Planta 207 163-171... 

Professor M. R. Maurya is currently heading the Department of Chemistry, IIT Roorkee. He has more than 26 years of teaching and research experience. He had worked in Loyola University of Chicago, USA, Iowa State University, Ames, Iowa, USA, National Chemical Laboratory, Pune, and Pune University Pune, before joining department of Chemistry at IIT Roorkee in 1996 and became full professor in 2008. His current area of research interests include structural and functional models of vanadate-dependent haloperoxidases, coordination polymers and their catalytic study, metal complexes encapsulated in zeolite cages and their catalytic study, polymer-anchored metal complexes and their catalytic study, and medicinal aspects of coordination compounds. So far, he has guided 21 doctoral and 7 Master s theses, co-authored more than 140 research papers in the international refereed journals. 

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