Mechanism of nitrite‐stimulated catalysis by lactoperoxidase
The reactions of lactoperoxidase (LPO) intermediates compound I, compound II and compound III, with nitrite ( ) were investigated. Reduction of compound I by was rapid (k2 = 2.3 × 107 m−1·s−1; pH = 7.2) and compound II was not an intermediate, indicating that radicals are not produced when reacts wi...
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Published in | European journal of biochemistry Vol. 268; no. 11; pp. 3214 - 3222 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Oxford, UK
Blackwell Science Ltd
01.06.2001
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Subjects | |
Online Access | Get full text |
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Summary: | The reactions of lactoperoxidase (LPO) intermediates compound I, compound II and compound III, with nitrite ( ) were investigated. Reduction of compound I by
was rapid (k2 = 2.3 × 107 m−1·s−1; pH = 7.2) and compound II was not an intermediate, indicating that
radicals are not produced when
reacts with compound I. The second‐order rate constant for the reaction of compound II with
at pH = 7.2 was 3.5 × 105 m−1·s−1. The reaction of compound III with
exhibited saturation behaviour when the observed pseudo first‐order rate constants were plotted against
concentrations and could be quantitatively explained by the formation of a 1 : 1 ratio compound III/NO2− complex. The Km of compound III for
was 1.7 × 10−4 m and the first‐order decay constant of the compound III/ complex was 12.5 ± 0.6 s−1. The second‐order rate constant for the reaction of the complex with
was 3.3 × 103 m−1·s−1. Rate enhancement by
does not require
as a redox intermediate.
accelerates the overall rate of catalysis by reducing compound II to the ferric state. With increasing levels of H2O2, there is an increased tendency for the catalytically dead‐end intermediate compound III to form. Under these conditions, the ‘rescue’ reaction of
with compound III to form compound II will maintain the peroxidatic cycle of the enzyme. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0014-2956 1432-1033 |
DOI: | 10.1046/j.1432-1327.2001.02213.x |