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Electron paramagnetic resonance spectroscopy signals attributable to low-spin haem c in the oxidised protein and [4Fe-4S]1+ in the dithionite-reduced protein were identified, at low temperature, in Thiosphaera pantotropha periplasmic nitrate reductase. Spin integration of these signals as well as elemental analysis suggest a stoichiometry of 1.3-1.6 c-haem and 1 [4Fe-4S] cluster per enzyme molecule. The Em (at pH 7.4) of the [4Fe-4S]2+,1+ couple, -160 mV, means that it is unlikely to be physiologically reducible. Peptide sequences from the 90 kDa subunit indicate that the enzyme is a member of the family of molybdopterin guanine dinucleotide-binding polypeptides, the majority of which possess a putative [4Fe-4S] cluster binding sequence and thus may also bind a (low potential) iron-sulphur cluster.

Original publication




Journal article



Publication Date





76 - 80


Amino Acid Sequence, Bacteria, Aerobic, Cell Membrane, Electron Spin Resonance Spectroscopy, Guanine Nucleotides, Heme, Iron-Sulfur Proteins, Molecular Sequence Data, Nitrate Reductase, Nitrate Reductases, Oxidation-Reduction, Peptide Fragments, Pterins, Sequence Analysis, Sequence Homology, Amino Acid