The Equilibrium of the Reaction Catalysed by Citrate Oxaloacetate-lyase.

1. A method of preparation and purification of citrate oxaloacetate-lyase (EC 4.1.3.6) from Aerobacter aerogenes is described. 2. The equilibrium of this reaction has been determined at pH 8.4 and 25 degrees . It has been shown that K, i.e. [citrate(3-)]/[oxaloacetate(keto) (2-)][acetate (-)], is 3.08+/-0.72, but that K(app.), i.e. [total citrate]/[total oxaloacetate][total acetate], is markedly affected by the initial concentrations of the reactants and magnesium. 3. The free-energy change during the cleavage of citrate has been calculated and compared with data from other sources. 4. The free energy of hydrolysis of acetyl-CoA has been evaluated from the present data. 5. A detailed knowledge of the interactions of the reactants with metal ions has been shown to be important in the calculation of the equilibrium constant and related thermodynamic functions.