Purification and biochemical characterization of tellurite-reducing activities from Thermus thermophilus HB8

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Abstract
Cell-free extracts of Thermus thermophilus HB8 catalyze the in vitro, NADH-dependent reduction of potassium tellurite (K2TeO3). Three different protein fractions with tellurite-reducing activities were identified. Two exhibited high molecular weight and were composed of at least two different polypeptides. The protein in the third fraction was purified to homogeneity and had a single polypeptide chain of 53 to 54 kilodaltons, with an isoelectric point of 8.1. Each enzyme was thermostable, the temperature optimum was 75 degrees C, and 30 mM NaCl, 1.5 M urea, or 0.004% sodium dodecyl sulfate caused 50% inhibition of the enzymes. However, 2% Triton X-100 did not have an inhibitory effect. The enzymes were also able to catalyze the reduction of sodium selenite and sodium sulfite in vitro. NADH was replaceable by NADPH. Divalent cations, such as Ca2+ and Ba2+, had no effect on the activity, while similar concentrations of Zn2+, Ni2+, and Cu2+ abolished the activity. This reductase activity could enable these bacteria both to reduce K2TeO3 and to increase their tolerance toward this salt.