||Mitochondrial Malate Dehydrogenase(MDH) is widely present in animals, plants, microorganisms and cultured cells. MDH in mitochondria is one of the key enzymes in the TCA cycle, catalyzing malate to form oxaloacetate; on the contrary, MDH in cytoplasm catalyzes oxaloacetate Forms malic acid. Oxaloacetate is an important intermediate product that connects many important metabolic pathways. Therefore, MDH plays an important role in a variety of cell physiological activities, including mitochondrial energy metabolism, malate-aspartate shuttle system, active oxygen metabolism, and disease resistance. According to different coenzyme specificities, MDH is divided into NAD-dependent MDH and NADP-dependent MDH. Bacteria usually only contain NAD-MDH. In eukaryotic cells, NAD-MDH is distributed in the cytoplasm and mitochondria. MDHm catalyzes the reduction of oxaloacetic acid by NADH to produce malic acid, resulting in a decrease in light absorption at 340nm.