Recognizes a protein of 150kDa, which is identified as the high molecular weight variant of Caldesmon. Two closely related variants of human caldesmon have been identified, which are different 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 has been detected in skeletal muscle. This MAb recognizes only the 150kDa variant (h-caldesmon) in Western blots of human aortic media extracts and is unreactive with fibroblast extracts from cultivated human foreskin. Caldesmon is a developmentally regulated protein involved in smooth muscle and non-muscle contraction.