Zeta’s mouse monoclonal antibody recognizes Caldesmon, a developmentally regulated protein involved in smooth muscle and non-muscle contraction. Two closely related variants of human Caldesmon have been identified which differ in their electrophoretic mobility and cellular distribution. The h-Caldesmon variant(120-150kDa) is predominantly expressed in smooth muscle whereas l-Caldesmon (70-80kDa) is found in non-muscle tissue and cells. Neither of the two variants of Caldesmon has been detected in skeletal muscle.