Characterization of the multiple catalytic activities of tartrate dehydrogenase

Tartrate dehydrogenase (TDH) has been purified to apparent homogeneity from Pseudomonas putida and has been demonstrated to catalyze three different NAD(+)-dependent reactions. TDH catalyzes the oxidation of (+)-tartrate to form oxaloglycolate and the oxidative decarboxylation of D-malate to form pyruvate and CO2. D-Glycerate and CO2 are formed from meso-tartrate in a reaction that is formally a decarboxylation with no net oxidation or reduction. The steady-state kinetics of the first two reactions have been investigated and found to follow primarily ordered mechanisms. The pH dependence of V and V/K was determined and indicates that catalysis requires that a base on the enzyme with a pK of 6.7 be unprotonated. TDH activity requires a divalent and a monovalent cation. Kinetic data suggest that the cations function in substrate binding and facilitation of the decarboxylation of beta-ketoacid intermediates.