Kinetics of the Incorporation of Tropoelastin into Elastic Fibers in Embryonic Chick Aortad

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Abstract
Matrix-free cells isolated by enzymic digestion of chick embryo aortas were labeled with [14C]proline for 20 to 60 min and the kinetics of the secretion of tropoelastin were followed by chasing the label and assaying [14C]tropoelastin in the cells and in the medium. The results indicated that secretion of tropoelastin followed the kinetics of a single first order process with a half time of 60 min. In parallel experiments tissue explants of chick embryo aortas were labeled with [14Clproine and the kinetics for the incorporation of tropoelastin into elastic fibers were followed by chasing the label and assaying the soluble [14C]tropoelastin and insoluble [14C]elastin in tissues. It was found that the incorporation of tropoelastin into elastic fibers also followed a single first order process with a half time of 85 min, similar to the secretion of tropoelastin from cells. In further studies, antibodies directed against tropoelastin were utilized to isolate soluble[14C]elastin components in the tissues after 0 to 4 hr chase of the 14CC label. The results demonstrated that all soluble elastin components were recovered as monomeric tropoelastin and no soluble oligomeric elastin could be detected. These results are consistent with the proposition that elastic fiber growth occurs by addition of individual tropoelastin molecules to existing fibers and that oligomers of elastin were not intermediates in the process.