Determination of half-reaction equilibrium in a ping-pong enzyme mechanism.

Substituted enzyme (or ping-pong) mechanisms usually involve enzymes that exist in two forms that alternate during the catalytic reaction. A method is described here for determining the position of the equilibrium of a half reaction in a ping-pong enzyme mechanism that is based on the kinetics of the burst reaction which occurs upon addition of reactants that recycle the enzyme from one form to another. The theoretical basis for the analysis is developed, and the method is applied to the half reaction of the aldimine form of aspartate transaminase with difluoro-oxaloacetate.