Identification of a 283-kDa protein component of the particulate matrix associated with cardiac mesenchyme formation

The elaboration of cardiac mesenchyme is controlled by a particulate form of extracellular matrix that is produced by the myocardium. This matrix consists of at least 7-10 major proteins or protein subunits. However, at present only a few of these proteins have been identified (i.e., ES130, fibronectin, transferrin). We report here the identification of a 283-kDa protein associated with this complex. This protein was identified using a new monoclonal antibody that is highly specific for this protein. The antibody does not react with human plasma fibronectin, chicken fibronectin or chicken cytotactin. In addition, this antibody inhibits the formation of mesenchyme when used in a bioassay of mesenchyme formation.