Studies of the Enzyme Fumarase. IV. The Dependence of the Kinetic Constants at 25° on Buffer Concentration, Composition and pH

The Michaelis constants and maximum steady-state velocities for the forward and reverse reactions catalyzed by fumarase depend upon the hydrogen ion concentration in a simple way in the range pH 5.5–8.5 when tris-(hydroxymethyl)-aminomethane acetate buffers are used. Altogether 10 kinetic parameters for the reaction at a particular buffer concentration may be calculated using the equations which have been derived earlier for the two Michaelis constants and two maximum steady-state velocities. The dependencies of these parameters on the concentration of tris-(hydroxymethyl)-aminomethane acetate and the effect of added sodium chloride have been determined. The “pH-independent” Michaelis constants are found to be a linear function of the acetate concentration.