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Redox Thermodynamics of the Fe(III)/Fe(II) Couple of Human Myeloperoxidase in Its High-Spin and Low-Spin Forms
- Source :
- Biochemistry. 45:12750-12755
- Publication Year :
- 2006
- Publisher :
- American Chemical Society (ACS), 2006.
-
Abstract
- Myeloperoxidase (MPO) (donor, hydrogen peroxide oxidoreductase, EC 1.11.1.7) is the most abundant neutrophil enzyme and catalyzes predominantly the two-electron oxidation of ubiquitous chloride (Cl-), to generate the potent bleaching oxidant hypochlorous acid (HOCl), thus contributing to bacterial killing and inflammatory reactions of neutrophils. Here, the thermodynamics of the one-electron reduction of the ferric heme in its ferric high-spin and cyanide-bound low-spin forms were determined through spectroelectrochemical experiments. The E(o)' values for free and cyanide-bound MPO (5 and -37 mV, respectively, at 25 degrees C and pH 7.0) are significantly higher than those of other heme peroxidases. Variable-temperature experiments revealed that the enthalpic stabilization of ferric high-spin MPO is much weaker than in other heme peroxidases and is exactly compensated by the entropic change upon reduction. In contrast to those of other heme peroxidases, the stabilization of the ferric cyanide-bound MPO is also very weak and fully entropic. This peculiar behavior is discussed with respect to the MPO-typical covalent heme to protein linkages as well as to the published structures of ferric MPO and its cyanide complex and the recently published structure of lactoperoxidase as well as the physiological role of MPO in bacterial killing.
- Subjects :
- Models, Molecular
Hypochlorous acid
Neutrophils
Protein Conformation
Entropy
Iron
Thermodynamics
Ferric Compounds
Biochemistry
chemistry.chemical_compound
Oxidoreductase
medicine
Humans
Ferrous Compounds
Myeloperoxidase redox thermodynamics reduction potential spectroelectrochemistry
Hydrogen peroxide
Heme
Peroxidase
chemistry.chemical_classification
Cyanides
biology
Lactoperoxidase
Electron Spin Resonance Spectroscopy
Kinetics
chemistry
Spectrophotometry
Myeloperoxidase
biology.protein
Ferric
Oxidation-Reduction
medicine.drug
Subjects
Details
- ISSN :
- 15204995 and 00062960
- Volume :
- 45
- Database :
- OpenAIRE
- Journal :
- Biochemistry
- Accession number :
- edsair.doi.dedup.....cf4fb527a7ce8075532eb81ee04ed6e2