Degrades an unidentified toxic product from the first step of tartrate degradation. (R)-glycerate + NAD(+) = 3-hydroxypyruvate + H(+) + NADH (R)-glycerate + NADP(+) = 3-hydroxypyruvate + H(+) + NADPH Carbohydrate acid metabolism; tartrate degradation; 3-hydroxypyruvate from D-glycerate: step 1/1. By tartrate.