Zinc Ions Inhibit the Qp Center of Bovine Heart Mitochondrial bc1 Complex by Blocking a Protonatable Group
| Autor: | Gebhard von Jagow, Thomas A. Link |
|---|---|
| Rok vydání: | 1995 |
| Předmět: |
Stereochemistry
chemistry.chemical_element Zinc Binding Competitive Biochemistry Redox Mitochondria Heart Electron Transport Complex III Cytochrome C1 Oxidoreductase Animals Binding site Molecular Biology chemistry.chemical_classification Binding Sites biology Ligand binding assay Cytochrome c Cell Biology Hydrogen-Ion Concentration Kinetics A-site chemistry biology.protein Cattle Oxidation-Reduction |
| Zdroj: | Journal of Biological Chemistry. 270:25001-25006 |
| ISSN: | 0021-9258 |
| DOI: | 10.1074/jbc.270.42.25001 |
| Popis: | Bovine heart bc1 complex is reversibly inhibited by zinc ions with an inhibition constant KI of 10(-7) M at pHor = 7.0. Binding of zinc is at least a factor of 10 tighter than binding of any other metal ion tested. Essentially complete inhibition of ubihydroquinone:cytochrome c oxidoreductase activity is observed at concentrations of [Zn2+]5 microM. Zinc does not affect the Km for the substrates, ubihydroquinone or cytochrome c, but zinc inhibits reduction of the cytochromes by ubihydroquinone through the QP center. A radioactive binding assay using 65Zn revealed one high affinity binding site per bc1 complex with KDor = 10(-7) M at pH = 7.0 and 3-4 additional low affinity binding sites (KD2 x 10(-6) M). Zinc binding does not depend on the redox state of the high potential chain (iron-sulfur protein and cytochrome c1). Zinc binds 3 times tighter to Fe-S-depleted bc1 complex indicating that the zinc binding site is not on the "Rieske" iron-sulfur protein in contrast to a recent report by Lorusso et al. (Lorusso, M., Cocco, T., Sardanella, A.M., Minuto, M., Bonomi, F., and Papa, S. (1991) Eur. J. Biochem. 197, 555-561). Zinc binds to a site which has the same affinity for zinc as for protons. We conclude that the zinc binding site is close to a protonatable group of the bc1 complex with pKa = 7.2 which has not been identified previously. We propose that this group is part of the proton channel at the hydroquinone oxidation center of the bc1 complex. |
| Databáze: | OpenAIRE |
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