BIOCHEMICAL-CHARACTERIZATION OF TELLURITE-REDUCING ACTIVITIES OF BACILLUS-STEAROTHERMOPHILUS-V

Bacillus stearothermophilus V is a naturally occurring Gram-positive r od which exhibits resistance to potassium tellurite, Crude extracts of this bacterium catalyse the NADH-dependent, protease-sensitive reduct ion of K2TeO3 in vitro. Two fractions which showed the ability to redu ce potassium tellurite (H1 and H2) were obtained. Fraction H1 behaved as a macroaggregate exhibiting a very high molecular mass that could n ot be estimated accurately. Upon electrophoresis in polyacrylamide gel s in the presence of SDS, however, it was resolved into three distinct bands of 60, 41 and 37.5 kDa. On the other hand, an M-r of 121 was de termined for fraction H2 by means of gel filtration and high-pressure liquid chromatography. In SDS-PAGE a unique protein band of 60 kDa was observed, suggesting that it is actually a dimer. Both fractions show ed pH and temperature optima of 7.5 and 57 degrees C, respectively. Co ncentrations of 2.5 M NaCl or 0.35 mM SDS inhibited fraction H2 almost completely, while fraction H1 retained 20% of its activity under the same conditions. Concentrations of 5 mM EDTA caused the activity of bo th fractions to increase 2-fold. In addition to reducing tellurite, th ey were also able to reduce Na2SeO3 and Na2SO3 in vitro.