A switch in heme axial ligation prepares Paracoccus pantotrophus cytochrome cd1 for catalysis.
Cytochrome cd1 nitrite reductase (cd1) from Paracoccus pantotrophus is a respiratory enzyme capable of using nitrite, hydroxylamine and oxygen as electron accepting substrates. Structural studies have shown that when the enzyme is reduced there is a change in the axial ligation of both hemes, which has been proposed to form part of the catalytic cycle. Here we report the use of a physiological electron donor, pseudoazurin, to investigate the relationship between heme ligation and catalysis. A combination of visible absorption and electron paramagnetic resonance spectroscopies reveals the formation of a catalytically competent state of oxidized cd1 with 'switched' axial ligands immediately after complete reoxidation of reduced cd1 with hydroxylamine. This activated conformer returns over 20 min at 25 degrees C to the state previously observed for oxidized 'as isolated' cd1, which is catalytically inactive towards the same substrates.[1]References
- A switch in heme axial ligation prepares Paracoccus pantotrophus cytochrome cd1 for catalysis. Allen, J.W., Watmough, N.J., Ferguson, S.J. Nat. Struct. Biol. (2000) [Pubmed]
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