Catalyzes the reversible oxidation of malate to oxaloacetate. Exhibits remarkably higher catalytic efficiency for oxaloacetate reduction than for malate oxidation in vitro. Highly specific for NAD(H). Can also use NADPH for oxaloacetate reduction, but catalytic efficiency is 97-fold higher with NADH. No activity detected with NADP(+) and malate. (S)-malate + NAD(+) = H(+) + NADH + oxaloacetate Strongly inhibited by Hg(2+) and Zn(2+). Activated by Na(+), NH(4)(+), Ca(2+), Cu(2+) and Mg(2+). kcat is 1181.6 sec(-1) for NADH-dependent reduction of oxaloacetate. kcat is 67.4 sec(-1) for NADPH-dependent reduction of oxaloacetate. kcat is 4.88 sec(-1) for NAD(+)-dependent oxidation of malate. Optimum pH is 8.0. Optimum temperature is 42 degrees Celsius. Belongs to the LDH/MDH superfamily. MDH type 2 family.