Has multiple catalytic activities. Apart from catalyzing the oxidation of (+)-tartrate to oxaloglycolate, also converts meso-tartrate to D-glycerate and catalyzes the oxidative decarboxylation of D-malate to pyruvate. NAD(+) + tartrate = 2-hydroxy-3-oxosuccinate + H(+) + NADH (2R,3S)-tartrate + NAD(+) = 2-hydroxy-3-oxosuccinate + H(+) + NADH (2R,3R)-tartrate + NAD(+) = 2-hydroxy-3-oxosuccinate + H(+) + NADH (2R,3R)-tartrate + H(+) = (R)-glycerate + CO2 (R)-malate + NAD(+) = CO2 + NADH + pyruvate Binds 1 Mg(2+) or Mn(2+) ion per subunit. Carbohydrate acid metabolism; tartrate degradation; 2-hydroxy-3-oxosuccinate from L-tartrate: step 1/1. Carbohydrate acid metabolism; tartrate degradation; 2-hydroxy-3-oxosuccinate from meso-tartrate: step 1/1. Carbohydrate acid metabolism; tartrate degradation; D-glycerate from L-tartrate: step 1/1. By tartrate. Belongs to the isocitrate and isopropylmalate dehydrogenases family.