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Changes in the Binding of Hydrogen Ions in Enzyme-Catalyzed Reactions

Robert A. Alberty
Organization: Massachusetts Institute of Technology
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Most enzyme-catalyzed reactions produce or consume hydrogen ions, and this is expressed by the change in the binding of hydrogen ions a in the reaction, as written in terms of reactants (sums of species). This property of a biochemical reaction is important because it determines the change in the apparent equilibrium constant K' with pH. There are two rather diffferent ways to calculate a for an enzyme-catalyzed reaction. The first, which has been used for a long time, involves calculating the partial derivative of the standard transformed Gibbs energy of reaction with respect to pH. The second, which is described and used in this package, involves calculating the average number of hydrogen atoms in each reactant and adding and subtracting these average numbers to obtain a. This package presents calculations of average numbers of hydrogen atoms in 199 biochemical reactants and uses them to calculate a for 229 enzyme-catalyzed reactions at 298.15 K and 0.25 M ionic strength. This database can be extended to include more reactants for which pKs are known or can be estimated.

*Science > Biology

biochemistry, thermodynamics, enzyme-catalyzed reactions, apparent equilibrium constants, binding of hydrogen ions
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changeHbind.nb (430 KB) - Mathematica Notebook [for Mathematica 5.2]