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Paracoccus pantotrophus cytochrome cd(1) is a physiological nitrite reductase and an in vitro hydroxylamine reductase. The oxidised "as isolated" form of the enzyme has bis-histidinyl coordinated c-heme and upon reduction its coordination changes to histidine/methionine. Following treatment of reduced enzyme with hydroxylamine, a novel, oxidised, conformer of the enzyme is obtained. We have devised protocols for freeze-quench near-ir-MCD spectroscopy that have allowed us to establish unequivocally the c-heme coordination of this species as His/Met. Thus it is shown that the catalytically competent, hydroxylamine reoxidised, form of P. pantotrophus cytochrome cd(1) has different axial ligands to the c-heme than "as isolated" enzyme.

Original publication




Journal article


Biochem Biophys Res Commun

Publication Date





674 - 677


Cytochromes, Electron Spin Resonance Spectroscopy, Freezing, Nitrite Reductases, Oxidation-Reduction, Paracoccus, Protein Conformation, Spectrophotometry, Infrared