Catalyzes the reversible oxidation of malate to oxaloacetate. Exhibits higher specific activity for oxaloacetate reduction than for malate oxidation in vitro. Has a strong preference for NAD. Can use NADPH for oxaloacetate reduction, but activity decreases more than 90%. No activity detected with NADP(+) and malate. (S)-malate + NAD(+) = H(+) + NADH + oxaloacetate Optimum pH is 10.0. Optimum temperature is above 92 degrees Celsius. Homotetramer. Belongs to the LDH/MDH superfamily.