Myosin is a hexamer of 2 identical heavy chains and 2 pairs of light chains. The two pairs of light chains of muscle myosins are called essential light chains (ELC) and regulatory light chains (RLC). The light chains stabilize the long alpha helical neck of the myosin head. Myosin light chain-2 (MYL2), also known as the regulatory light chain of myosin, is an important protein involved in the regulation of myosin ATPase activity. Calcium triggers the phosphorylation of MYL2 that in turn triggers contraction. Defects in MYL2 are the cause of cardiomyopathy familial hypertrophic type 10 and mid-left ventricular chamber type 2. An increase in ventricular MYL2 is observed during myocardial hypertrophy in cardiac patients with valve stenosis. This antibody reacts with cardiac and skeletal muscle.