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A cysteine desulfurase protein,IscS,was encoded by the operon iscSUA in Acidithiobacillus ferrooxidans.The gene of IscS from Acidithiobacillus ferrooxidans ATCC 23270 was cloned and expressed in Escherichia coli.The protein was purified by one-step affinity chromatography to homogeneity.The final protein yield after affinity chromatography was 12.9%.The enzyme was characterized for thermal stability,pH and kinetic parameters.The molecular mass of recombinant IscS was 46 ku by SDS-PAGE.The optimum pH was 8.0-8.5.The enzyme had a temperature optimum at 30 ℃ and was relatively stable at 40 ℃,with 67% loss of activity.1,5-I-AEDANS significantly inhibited IscS activity.Kinetic parameters Km and Vmax were found to be 0.11 mmol/L and 2.57 μmol/(L-min).