Electrostatic facilitation of the reaction catalyzed by the manganese-containing and the iron-containing superoxide dismutases |
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Authors: | Jeffrey Benovic Tommy Tillman Amelia Cudd Irwin Fridovich |
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Affiliation: | Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710 USA |
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Abstract: | Both the iron-containing and the manganese-containing superoxide dismutases from Escherichia coli show diminished activity with increasing ionic strength, indicative of electrostatic facilitation of the catalyzed reaction. Since both enzymes bear a net negative charge at the assay pH, as does the substrate, this suggests a cationic locale in the active site region. Acetylation of the enzymes inverted their response to increasing ionic strength. It thus appears that lysine residues provide the observed electrostatic facilitation. A specific inhibition by large monovalent anions was observed with the iron-containing superoxide dismutase and was taken to indicate the presence of a cationic group, within a hydrophobic crevice, at the active site. |
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Keywords: | Author to whom correspondence should be addressed. |
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