Calculation of equilibrium compositions of systems of enzyme-catalyzed reactions.

When a system of enzyme-catalyzed reactions does not involve H(2)O as a reactant, the equilibrium composition at specified temperature, pH, and ionic strength can be calculated using the Mathematica programs equcalcc, which uses the conservation matrix, or equcalcrx, which uses the stoichiometric number matrix. When H(2)O is involved as a reactant, equcalcrx must be used because H(2)O is not in the stoichiometric number matrix. It is shown here that the use of equcalcrx is equivalent to using the further transformed Gibbs energy G" that eliminates oxygen from the conservation matrix. Calculations presented here show that the calculation of further transformed Gibbs energies of formation of reactants other than coenzymes can be avoided by using equcalcrx to calculate equilibrium concentrations.