Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 277, Issue 5, Pages 3471-3476Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M107974200
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- NIGMS NIH HHS [GM 38237, R01 GM038237] Funding Source: Medline
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Recent kinetics experiments using mutants of the bc(1) complex (ubihydroquinone-cytochrome c oxidoreductase) iron-sulfur subunit with modified hinge regions have revealed the crucial role played by the large scale movement of its [2Fe-2S] cluster domain during the activity of this enzyme. In particular, one of these mutants (+1Ala) with an insertion of one alanine residue in the hinge region is partially deficient in performing this movement. We found that this defect can be overcome by the appearance of a second mutation substituting the leucine at position 286 in the ef loop of cytochrome b with a phenylalanine. Detailed studies of these mutants and their derivatives revealed that the ef loop acts as a barrier that needs to be crossed for multiple turnovers of the enzyme but not for a single turnover ubihydroquinone oxidation site catalysis. These findings indicate that the movement of the iron-sulfur subunit is composed of two discrete parts: a micro-movement at the cytochrome b interface, during which the [2Fe-2S] cluster interacts with ubihydroquinone oxidation site occupants and catalyzes ubihydroquinone oxidation, and a macro-movement, during which the cluster domain swings away from cytochrome b interface, crosses the ef loop, and reaches a position close to cytochrome c(1) heme, to which it ultimately transfers an electron.
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