Is Newly-Secreted Elastin Cleaved to a Smaller Molecule Before Being Incorporated Into Crosslinked Elastin Fibers?

Abstract

The biosynthesis of elastin was examined in matrix-free cells isolated by enzymic digestion of aortas from 17 day old chick embryos. When the cells were incubated with (¹⁴C) proline and then were rapidly boiled in buffer containing high concentrations of protease inhibitors and sodium dodecyl sulfate, about one-quarter of the intra-cellular ¹⁴C-protein was recovered as an elastin component with an apparent molecular weight of about 72,000. Examination of the medium from the cell suspension indicated that the largest elastin component secreted by the cells also had an apparent molecular weight of about 72,000.

Experiments with intact aorta were carried out in order to study the conversion of the elastin component of 72,000 daltons to crosslinked fibers. Pulse-chase experiments indicated that about two-thirds of the component was converted to crosslinked material in 2 hours. When the tissues were incubated with either penicillamine or β-aminopropionitrile, the conversion to insoluble fibers was inhibited. With penicillamine, the elastin component remained in the tissue as a Polypeptide of about 72,000 daltons for up to 5 hours. With β-aminopropionitrile, the elastin component of 72,000 daltons persisted for about 2 hours, but thereafter it was gradually degraded to small peptides which were recovered in the incubation medium. The results suggest that the elastin component synthesized and secreted by cells in chick aorta is incorporated into elastin fibers without cleavage to a protein of considerably smaller size.