A Kinetic and Equilibrium Analysis of the Glutamic Oxaloacetate Transaminase Mechanism

Abstract

The amino group carrier function of the coenzyme of transamination was postulated on the basis of coenzyme properties and model experiments (1, 2) and was established for the enzymatic reaction by the observation that pyridoxal and pyridoxamine phosphates exhibit equivalent activity in the reactivation of crude apoglutamate oxaloacetate transaminase (3) and by direct spectrophotometric observation of the coenzyme interconversion in experiments on the purified enzyme (4). The enzyme is stable and highly active and catalyzes a reaction that is susceptible to detailed kinetic analysis by continuous optical methods. Moreover, the bound coenzyme exhibits spectral changes that make it an indicator of events occurring in experiments carried out with substrate level concentrations of enzyme. It is therefore possible to attempt the correlation of mechanism and intermediary reaction equilibria, deduced kinetically, with results obtained by examination of the bound coenzyme itself under various conditions. The glutamate oxaloacetate enzyme is a mechanistic prototype for a large number of experimentally less accessible transaminases and also for the general class of group-transferring enzymes, which operate exclusively through binary enzyme substrate complexes.