The purification and some properties of rusticyanin, a blue copper protein involved in iron(II) oxidation from Thiobacillus ferro-oxidans

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Abstract
The ‘blue’ copper-containing protein rusticyanin was purified to homogeneity from cells of the chemolithotrophic bacterium Thiobacillus ferro-oxidans by (NH4)SO4 fractionation and ion-exchange chromatography. The protein, which is stable at low pH, consists of a single polypeptide chain of mol. wt. 16500 and possesses 0.79 (+/- 0.28)g-atom of Cu/mol. The protein, which does not contain arginine residues, has optical absorbance maxima at 287, 450, 597 and 750 nm and is generally similar to azurin. The isolated protein is reduced directly by Fe2+ with a 1:1 stoicheiometry to Cu. On reduction by Fe2+ the absorption peaks at 450, 597 and 750 nm are abolished, with the appearance of a new absorption band at 320 nm. The results obtained are consistent with rusticyanin being the initial acceptor of electrons from Fe2+ during respiratory iron oxidation.