Abstract
The kinetics of hydrolysis of the inorganic (PPi) and organic (ATP) substrates by Escherichia coli inorganic pyrophosphatase (PPase) and its mutant forms with Asp42 replaced by Ala, Asn, or Glu was studied. The Mn2+ or Zn2+ ions were used as activators of the enzymatic reaction. The kinetic parameters of hydrolysis were determined. The inhibitory effect of these cations on substrate hydrolysis was investigated. The dissociation constants were calculated for the Mn2+- and Zn2+-binding activator and inhibitor subsites of E. coli PPase. The observed hydrolysis rate of PPi increases in the series Zn2+ < Mn2+ < Mg2+, whereas the potential efficiency of these cations decreases in this series. Hydrolysis of ATP by E. coli PPase occurs only in the presence of Mn2+. The reasons for the observed differences in the substrate specificity of the enzyme are discussed.
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