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Polythionate degradation by tetrathionate hydrolase of Thiobacillus ferrooxidans

Department of Microbiology and Enzymology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands

²Author for correspondence: J. Gijs Kuenen. Tel: +31 152 785308. Fax: +31 IS2 782355.

ABSTRACT

Cell-free extracts of Thiobacillus ferrooxidans grown with thiosulfate as energy source and prepared at high ammonium sulfate concentrations and at low pH are capable of polythionate hydrolysis. The enzyme responsible for the hydrolysis of tetrathionate (S₄O^2-₆) and pentathionate (S₄O^2-₆) was purified to homogeneity. Enzyme activity during the purification procedure was based on a continuous spectrophotometric method that detects soluble intermediates that absorb in the UV region. The end products of hydrolysis of both polythionates by the pure enzyme were thiosulfate, sulfur and sulfate. The purified enzyme has a pH optimum of around 4 and a temperature optimum of 65 °. The activity is strongly influenced by the presence of sulfate ions. The purified enzyme is a dimer with two identical subunits of molecular mass 52 kDa. During purification of tetrathionate hydrolase, fractions able to hydrolyse trithionate and tetrathionate were separated, indicating that the two substrates are hydrolysed by different enzymes.

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