Nitroxide radicals as research tools : Elucidating the kinetics and mechanisms of catalase-like and "suicide inactivation" of metmyoglobin
Copyright © 2016 Elsevier B.V. All rights reserved..
BACKGROUND: Metmyoglobin (MbFe(III)) reaction with H(2)O(2) has been a subject of study over many years. H(2)O(2) alone promotes heme destruction frequently denoted "suicide inactivation," yet the mechanism underlying H(2)O(2) dismutation associated with MbFe(III) inactivation remains obscure.
METHODS: MbFe(III) reaction with excess H(2)O(2) in the absence and presence of the nitroxide was studied at pH 5.3-8.1 and 25°C by direct determination of reaction rate constants using rapid-mixing stopped-flow technique, by following H(2)O(2) depletion, O(2) evolution, spectral changes of the heme protein, and the fate of the nitroxide by EPR spectroscopy.
RESULTS: The rates of both H(2)O(2) dismutation and heme inactivation processes depend on [MbFe(III)], [H(2)O(2)] and pH. Yet the inactivation stoichiometry is independent of these variables and each MbFe(III) molecule catalyzes the dismutation of 50±10 H(2)O(2) molecules until it is inactivated. The nitroxide catalytically enhances the catalase-like activity of MbFe(III) while protecting the heme against inactivation. The rate-determining step in the absence and presence of the nitroxide is the reduction of MbFe(IV)O by H(2)O(2) and by nitroxide, respectively.
CONCLUSIONS: The nitroxide effects on H(2)O(2) dismutation catalyzed by MbFe(III) demonstrate that MbFe(IV)O reduction by H(2)O(2) is the rate-determining step of this process. The proposed mechanism, which adequately fits the pro-catalytic and protective effects of the nitroxide, implies the intermediacy of a compound I-H(2)O(2) adduct, which decomposes to a MbFe(IV)O and an inactivated heme at a ratio of 25:1.
GENERAL SIGNIFICANCE: The effects of nitroxides are instrumental in elucidating the mechanism underlying the catalysis and inactivation routes of heme proteins.
| Medienart: |
E-Artikel |
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| Erscheinungsjahr: |
2016 |
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| Erschienen: |
2016 |
| Enthalten in: |
Zur Gesamtaufnahme - volume:1860 |
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| Enthalten in: |
Biochimica et biophysica acta - 1860(2016), 7 vom: 15. Juli, Seite 1409-16 |
| Sprache: |
Englisch |
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| Beteiligte Personen: |
Samuni, Uri [VerfasserIn] |
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| Links: |
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| Anmerkungen: |
Date Completed 10.08.2016 Date Revised 26.11.2016 published: Print-Electronic Citation Status MEDLINE |
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| doi: |
10.1016/j.bbagen.2016.04.002 |
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| Förderinstitution / Projekttitel: |
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| PPN (Katalog-ID): |
NLM259253464 |
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| 100 | 1 | |a Samuni, Uri |e verfasserin |4 aut | |
| 245 | 1 | 0 | |a Nitroxide radicals as research tools |b Elucidating the kinetics and mechanisms of catalase-like and "suicide inactivation" of metmyoglobin |
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| 500 | |a Date Completed 10.08.2016 | ||
| 500 | |a Date Revised 26.11.2016 | ||
| 500 | |a published: Print-Electronic | ||
| 500 | |a Citation Status MEDLINE | ||
| 520 | |a Copyright © 2016 Elsevier B.V. All rights reserved. | ||
| 520 | |a BACKGROUND: Metmyoglobin (MbFe(III)) reaction with H(2)O(2) has been a subject of study over many years. H(2)O(2) alone promotes heme destruction frequently denoted "suicide inactivation," yet the mechanism underlying H(2)O(2) dismutation associated with MbFe(III) inactivation remains obscure | ||
| 520 | |a METHODS: MbFe(III) reaction with excess H(2)O(2) in the absence and presence of the nitroxide was studied at pH 5.3-8.1 and 25°C by direct determination of reaction rate constants using rapid-mixing stopped-flow technique, by following H(2)O(2) depletion, O(2) evolution, spectral changes of the heme protein, and the fate of the nitroxide by EPR spectroscopy | ||
| 520 | |a RESULTS: The rates of both H(2)O(2) dismutation and heme inactivation processes depend on [MbFe(III)], [H(2)O(2)] and pH. Yet the inactivation stoichiometry is independent of these variables and each MbFe(III) molecule catalyzes the dismutation of 50±10 H(2)O(2) molecules until it is inactivated. The nitroxide catalytically enhances the catalase-like activity of MbFe(III) while protecting the heme against inactivation. The rate-determining step in the absence and presence of the nitroxide is the reduction of MbFe(IV)O by H(2)O(2) and by nitroxide, respectively | ||
| 520 | |a CONCLUSIONS: The nitroxide effects on H(2)O(2) dismutation catalyzed by MbFe(III) demonstrate that MbFe(IV)O reduction by H(2)O(2) is the rate-determining step of this process. The proposed mechanism, which adequately fits the pro-catalytic and protective effects of the nitroxide, implies the intermediacy of a compound I-H(2)O(2) adduct, which decomposes to a MbFe(IV)O and an inactivated heme at a ratio of 25:1 | ||
| 520 | |a GENERAL SIGNIFICANCE: The effects of nitroxides are instrumental in elucidating the mechanism underlying the catalysis and inactivation routes of heme proteins | ||
| 650 | 4 | |a Journal Article | |
| 650 | 4 | |a Research Support, Non-U.S. Gov't | |
| 650 | 4 | |a Compound II | |
| 650 | 4 | |a Heme protein | |
| 650 | 4 | |a Kinetics | |
| 650 | 4 | |a Mechanism | |
| 650 | 4 | |a Nitroxide | |
| 650 | 4 | |a Suicide inactivation | |
| 650 | 7 | |a Nitrogen Oxides |2 NLM | |
| 650 | 7 | |a Metmyoglobin |2 NLM | |
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| 700 | 1 | |a Czapski, Gideon |e verfasserin |4 aut | |
| 700 | 1 | |a Goldstein, Sara |e verfasserin |4 aut | |
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