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. 1977 Jul 1;165(1):71–79. doi: 10.1042/bj1650071

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

M E McAdam, R A Fox, F Lavelle, E M Fielden
PMCID: PMC1164870  PMID: 889577

Abstract

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

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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