Haloperoxidases Chloroperoxidase

Because the reactivity of a cyclopropane closely resembles that of an olefinic double bond [2], haloperoxidases (chloroperoxidase from Cadariomyces fumago, bromoperoxidase from Penicillus capitalus) add readily to the ring of cyclopropanes la,b in the presence of halide ions and hydrogen peroxide to... 

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. 

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. 

The ubiquitous hemoprotein chloroperoxidase (CPO) (1) continues to be of great mechanistic and practical interest following its isolation more than 40 years ago from Caldariomyces fumago (2138). The CPO gene from this filamentous fungus has been isolated and sequenced (2139), an active recombinant CPO has been produced (2140), and the crystal structure of this CPO has been determined (2141, 2142). The fungus Curvularia inaequalis contains a vanadium CPO, which has been characterized (primary and X-ray structure) (Fig. 4.1) (2143-2147), as has the vanadium haloperoxidase from Corallina officinalis (2324). This enzyme has also been studied by density functional theory lending support to the proposed mechanism of action (Scheme 4.1) (2325). A related vanadium CPO, which shares 68% primary structural identity with the Curvularia inaequalis CPO, is produced... 

Recently the amino acid sequence of vanadium chloroperoxidase was determined to have similar stretches with three families of acid phosphatases, which were previously considered unrelated [72], This sequence raises questions about the phosphatase activity of apo-V-ClPO and whether the acid phosphatases can coordinate vanadate and carry out peroxidative halogenation chemistry. In fact, apo-V-C1PO does have phosphatase activity, catalyzing the hydrolysis of/i-nitrophe-nol phosphate (p-NPP). In addition, /i-NPP displaces vanadate from V-CIPO. At this point, the haloperoxidase activity of the acid phosphatases containing coordinated vanadium(V) has not been reported. 

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... 

Messershmidt, A., L. Prade, and R. Wever. 1998. Chloroperoxidase from Curvularia inaequalis x-ray structures of native and peroxide form reveal vanadium chemistry in vanadium haloperoxidases. ACS Symp. Ser. 711 186-201. 

The specific chloroperoxidase, bromoperoxidase, and iodoperoxi-dase activities differ substantially and depend on pH and the concentrations of halide and hydrogen peroxide (2). In general, the specific activity for halide oxidation increases in the order of chloride, bromide, and iodide. The pH for maximum specific haloperoxidase activity generally decreases in the order of iodide, bromide, and chloride, but direct comparisons are difficult because the pH maximum can be shifted over several pH units by varying the ratio of halide to hydrogen peroxide and because both halide and hydrogen peroxide can inhibit the enzyme under certain conditions. 

The X-ray structures of vanadium bromoperoxidases from the red seaweeds Corallina pilulifera and C. officinalis have also been determined and their structures are almost identical. The native structure of these enzymes is dodecameric and the structure is made up of 6 homo-dimers. The secondary stmcture of the chloroperoxidase from the ftmgus Curvularia inaequalis that will be discussed later can be superimposed with the Corallina hromoperoxidase dimer. Many of the a helices of each chloroperoxidase domain are structurally equivalent to the a helices in the Corallina hromoperoxidase dimer. This is in line with the evolutionary relationship between the haloperoxidases that will be discussed later. The disulfide bridges in the enzyme from A. nodosum are not found in the enzyme from Corallina and the two remaining cysteine residues are not involved in disulfide bonds. Additionally, in this enzyme binding sites are present for divalent cations that seem to be necessary to maintain the stmcture of the active site cleft. All the residues directly involved in the binding of vanadate are conserved in the algal bromoperoxidases. ... 

Organisms containing vanadate-dependent haloperoxidases. The enzymes from the algae A. nodosum and Cor. officinalis and the lichen X parietina are hromoperoxidases, and the fungal enzyme (Cur. inaequalis, shown with sporangia) is a chloroperoxidase. 

Jumago, are easily obtained. Chloroperoxidase can also be obtained in larger quantities from the fungus Curvularia inaequalisi40K Thus, a number of different haloperoxidases from various sources are available in quantities necessary for the enzymatic halogenation of organic compounds. 

Phenols and phenol ethers are very good substrates for haloperoxidases. The first aromatic substrate to be used in enzymatic iodination was tyrosine. This substrate was iodinated using chloroperoxidase from Caldariomyces Jumago1441 and thyroid peroxidase1451. Horseradish peroxidase and lactoperoxidase have been used to lable proteins with radioactive isotopes of iodide111 and bromoperoxidase from Penicillus capitatus has been employed to lable human serum albumin with the radioactive isotope of bromine1461. 

The most intensively studied haloperoxidases are the chloroperoxidase from the mold Caldariomyces fumago [1322] and bromoperoxidases fi om algae [1764] and bacteria such as Pseudomonas aureofaciens [1765], Ps. pyrrocinia [1766], and Streptomyces sp. [1767]. The only iodoperoxidase of preparative use is isolated from horseradish root [1768]. A haloperoxidase isolated from milk has been reported to be useful for the formation of halohydrins [1769]. 

Haloperoxidases have been shown to transform alkenes by a formal addition of hypohalous acid to produce halohydrins. The reaction mechanism of enzymatic halogenatitHi has been debated for some time and it is now accepted that it proceeds via a halonium intermediate [1770, 1771], similar to the chemical formation of halohydrins (Scheme 2.228). The former species is derived from hypohalous acid or molecular halogen, which is in turn produced by the enzyme via oxidation of halide [1772]. In support of this, a HOCl-adduct of Fe -protoporphyrin IX was identified as a direct enzyme-halogen intermediate involved in chloroperoxidase-catalyzed halogenaticHi [1773]. 

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