>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 [4F–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.
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机译：鉴定了氧化蛋白中低自旋血红素 c 和连二亚硫酸盐还原蛋白中的[4Fe-4S] 1 + 引起的>电子顺磁共振波谱信号，在低温下， Thiosphaera pantotropha 周质硝酸还原酶中。这些信号的自旋整合以及元素分析表明，每个酶分子的化学计量为1.3–1.6 c -血红素和1 [4Fe-4S]簇。 [4F–4S] 2 +，1 + 对的 E m （在pH 7.4时）为-160 mV，表示它不太可能是生理可还原的。来自90 kDa亚基的肽序列表明该酶是钼蝶呤鸟嘌呤二核苷酸结合多肽家族的成员，其中大多数具有推定的[4Fe–4S]簇结合序列，因此也可能结合（低电位）铁-硫簇。
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