<p>Malate dehydrogenase (<db_xref db="EC" dbkey="1.1.1.37"/>) (MDH) [<cite idref="PUB00000626"/>] catalyzes the interconversion of malate to oxaloacetate utilizing the NAD/NADH cofactor system. The enzyme participates in the citric acid cycle and exists in all aerobics organisms.</p> <p>While prokaryotic organisms contains a single form of MDH, in eukaryotic cells there are two isozymes: one which is located in the mitochondrial matrix and the other in the cytoplasm. Fungi and plants also harbor a glyoxysomal form which functions in the glyoxylate pathway. In plants chloroplast there is an additional NADP-dependent form of MDH (<db_xref db="EC" dbkey="1.1.1.82"/>) which is essential for both the universal C3 photosynthesis (Calvin) cycle and the more specialised C4 cycle.</p> <p>The pattern for this enzyme includes two residues involved in the catalytic mechanism [<cite idref="PUB00000309"/>]: an aspartic acid which is involved in a proton relay mechanism, and an arginine which binds the substrate.</p>