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 f orm of extracellular matrix that is produced by the myocardium. This m atrix consists of at least 7-10 major proteins or protein subunits. Ho wever, at present only a few of these proteins have been identified (i .e., ES130, fibronectin, transferrin). We report here the identificati on of a 283-kDa protein associated with this complex. This protein was identified using a new monoclonal antibody that is highly specific fo r this protein. The antibody does not react with human plasma fibronec tin, chicken fibronectin or chicken cytotactin. In addition, this anti body inhibits the formation of mesenchyme when used in a bioassay of m esenchyme formation.