Lactate dehydrogenase is an enzyme that catalysis the conversion of lactate to pyruvic acid and vice versa. It is made up of four subunits. The two most common subunits are the LDH-M and LDH-H protein. Five possible isoenzymes can form from these two subunits: 4H, 4M, and the three mixed tetramers (3H1M, 2H2M, 1H3M).Although these five forms are enzymatically similar they are distributed differently in various tissue. The major isoenzymes of skeletal muscle, M4, has four muscle (M) subunits. The major isoenzymes for heart muscle in most species is H4 containing four heart (H) subunits.in myocardial infarction the H4 slightly increases occur in high concentration in myocardium and in red
