POLYTHIONATE DEGRADATION BY TETRATHIONATE HYDROLASE OF THIOBACILLUS-FERROOXIDANS

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 resp onsible for the hydrolysis of tetrathionate (S4O62-) and pentathionate (S5O62-) was purified to homogeneity. Enzyme activity during the puri fication 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 we re thiosulfate, sulfur and sulfate. The purified enzyme has a ph optim um of around 4 and a temperature optimum of 65 degrees C. 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 hy drolyse trithionate and tetrathionate were separated, indicating that the two substrates are hydrolysed by different enzymes.