This antibody recognizes human myosin regulatory light chain (MRLC), also known as MYL9 and LC20.

Myosin is a hexamer composed of two high molecular weight heavy chains and four light chain subunits, which include two alkali light chains and two MRLCs. MRLC functions to stabilize the myosin heavy chain, and may also modulate the availability of cross bridges to bind to actin. Phosphorylation of the MRLC by myosin light chain kinase (MLCK) is necessary for smooth muscle contraction via activating myosin ATPase.