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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
 
 
 

Two-electron reduction and one-electron oxidation of organic hydroperoxides by human myeloperoxidase.

The reaction of native myeloperoxidase ( MPO) and its redox intermediate compound I with hydrogen peroxide, ethyl hydroperoxide, peroxyacetic acid, t-butyl hydroperoxide, 3-chloroperoxybenzoic acid and cumene hydroperoxide was studied by multi-mixing stopped-flow techniques. Hydroperoxides are decomposed by MPO by two mechanisms. Firstly, the hydroperoxide undergoes a two-electron reduction to its corresponding alcohol and heme iron is oxidized to compound I. At pH 7 and 15 degrees C, the rate constant of the reaction between 3-chloroperoxybenzoic acid and ferric MPO was similar to that with hydrogen peroxide (1.8x10(7) M(-1) s(-1) and 1.4x10(7) M(-1) s(-1), respectively). With the exception of t-butyl hydroperoxide, the rates of compound I formation varied between 5.2x10(5) M(-1) s(-1) and 2.7x10(6) M(-1) s(-1). Secondly, compound I can abstract hydrogen from these peroxides, producing peroxyl radicals and compound II. Compound I reduction is shown to be more than two orders of magnitude slower than compound I formation. Again, with 3-chloroperoxybenzoic acid this reaction is most effective (6. 6x10(4) M(-1) s(-1) at pH 7 and 15 degrees C). Both reactions are controlled by the same ionizable group (average pK(a) of about 4.0) which has to be in its conjugated base form for reaction.[1]

References

  1. Two-electron reduction and one-electron oxidation of organic hydroperoxides by human myeloperoxidase. Furtmüller, P.G., Burner, U., Jantschko, W., Regelsberger, G., Obinger, C. FEBS Lett. (2000) [Pubmed]
 
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