Lactate dehydrogenase is also known as L-lactate dehydrogenase A chain, LDH-A, LDH muscle subunit and LDH-M. Two isozymes of LDH occur in mammals, LDH-M and LDH-H which come together to form a homotetramer of 36kD subunits. Every LDH molecule consists of four subunits, where each subunit is either H each M (based on their electrophoretic properties.) There are, therefore, five LDH isotypes: LDH-1 (4H)-in the heart, LDH-2 (3H1M)-in the reticuloendothelial system, LDH-3 (2H2M)-in the lungs, LDH-4 (1H3M)-in the kidneys and LDH-5 (4M) in the liver and striated muscle. Usually LDH-2 is the predominant form in the serum. An LDH-1 level higher than the LDH-2 level (a flipped pattern) suggests myocardial infarction (damage to heart tissues releases heart LDH, which is rich in LDH-1, into the bloodstream). In general, LDH is often used as a marker of tissue breakdown. LDH shows a cytoplasmic localization. Source: Human Erythrocytes Unit Definition: One unit will catalyze the oxidation of one mi