METABOLISM OF TETRATHIONATE IN THIOBACILLUS-ACIDOPHILUS

Cell-free extracts of Thiobacillus acidophilus catalysed the stoichiom etric conversion of tetrathionate to thiosulphate, sulphur and two pro tons. The pH optimum of the enzyme activity was 3.0 and its temperatur e optimum 40-degrees-C. The enzyme was unstable at 30 and 40-degrees-C , at which its activity decreased to zero within 100 and 20 h, respect ively. Enzyme activity was not affected by incubation for 1 week on ic e or by freezing and thawing of the extract. The K(m) for tetrathionat e was 0.3 mM. Enzyme activity was stimulated by ammonium sulphate up t o a concentration of 1 M. The results indicate that trithionate hydrol ase cannot account for the observed conversion of tetrathionate.