Malate dehydrogenase. Has no activity with NADPH as substrate. Does not show lactate dehydrogenase activity. (S)-malate + NAD(+) = H(+) + NADH + oxaloacetate By arsenate for both the forward and reverse reactions. kcat is 47.4 sec(-1) for L-malate. kcat is 385.6 sec(-1) for NAD. kcat is 665.34 sec(-1) for oxaloacetate. kcat is 962.66 sec(-1) for NADH. Optimum pH is 7.6 for oxaloacetate reduction and 9.6 for malate oxidation (PubMed:21439955, PubMed:19277715). Stable between pH 6.8-8.5 for the forward reaction (PubMed:19277715). Has highest activity between 5-40 degrees Celsius. No activity at 60 degrees Celsius. Homodimer. Belongs to the LDH/MDH superfamily. MDH type 2 family.