Cytochrome cd1 from Parococcus pantotrophus exhibits kinetically gated, conformationally dependent, highly cooperative two-electron redox behavior

A Koppenhofer, Karen L Turner, James W A Allen, Stephen K Chapman, Stuart J Ferguson

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    43 Citations (Scopus)

    Abstract

    Each monomer of the dimeric cytochrome cd(1) nitrite reductase from Paracoccus pantotrophus contains two hemes: one c-type center and one noncovalently bound dr center. Potentiometric analysis at 20 degrees C shows substantial cooperativity between the two redox centers in terms of their joint co-reduction (or co-oxidation) at a single apparent potential with an n value of 1.4 +/- 0.1. Reproducible hysteresis is demonstrated in the redox titrations. In a reductive titration both centers titrate with an apparent midpoint potential of +60 +/- 5 mV while in the oxidative titration the apparent potential is +210 +/- 5 mV. However, at 40 degrees C the reductive and oxidative titrations are shifted such that they almost superimpose; each has n = 2. A kinetically gated process that can be correlated with oxidation/reduction-dependent ligand changes at the two heme centers, previously seen by crystallography, is implicated. In contrast, a semi-apoenzyme, lacking the dl heme, exhibits a reversible redox titration with a midpoint potential of +242 +/- 5 mV (n = 1). The data with the holoenzyme show how redox changes can themselves generate a gating of the type that is minimally required to account for redox-linked proton pumping by membrane-bound cytochromes.

    Original languageEnglish
    Pages (from-to)4243-4249
    Number of pages7
    JournalBiochemistry
    Volume39
    Issue number15
    DOIs
    Publication statusPublished - 18 Apr 2000

    Keywords

    • AERUGINOSA NITRITE REDUCTASE
    • C-HEME
    • MAGNETIC-PROPERTIES
    • PROTEIN
    • PURIFICATION
    • 3FE-4S CLUSTERS
    • OXIDASE
    • PSEUDOMONAS-AERUGINOSA
    • AXIAL LIGAND REPLACEMENT
    • THIOSPHAERA-PANTOTROPHA

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