A pulse-radiolysis study of the manganese-containing superoxide dismutase from Bacillus stearothermophilus. A kinetic model for the enzyme action.

摘要: The enzymic reaction mechanism of a manganese-containing superoxide dismutase from Bacillus stearothermophilus was studied by using pulse radiolysis. During catalysis (pH 8.9; 25 degrees C), changes occurring in the kinetics substrate disappearance and visible absorption enzyme at 480 nm established that simple two-step found for copper- iron-containing dismutases is not involved. At low ratio (less than 15) concentration to decay O2--is close exponetial, whereas much higher ratios (greater 100) observed predominantly zero-order. simplest interpretation results invokes rapid one-electron oxidation-reduction cycle ('the fast cycle') and, concurrently, slower giving form essentially unreactive towards O2-- but which undergoes first-order yield fully active native slow cycle'). involves EA EB can be obtained also treating with H2O2. Computer calculations made such model predict behaviour excellent agreement results.