A High Molecular Weight Species of Soluble Elastin-Proelastin

Abstract

The isolation of a high molecular weight species (130–140,000 daltons) of soluble elastin from the aortae of lathyritic chicks is described. In comparison to chick tropoelastin, the higher molecular weight material possesses an increased amount of acidic and hydroxyl amino acids and in contrast to tropoelastin, contains histidine, methionine and cystine residues. This high molecular weight species of soluble elastin is susceptible to proteolytic degradation and can be shown to readily break down to lower molecular weight components including tropoelastin. Preliminary data suggest that collagen may have a protective effect on the cleavage of the high molecular weight protein pointing to a potentially significant interaction between the two main structural proteins.

Immunoelectrophoresis of the high molecular weight soluble elastin reveals that it is electrophoretically distinct from tropoelastin yet it is immunochemically related or identical.

Ion exchange chromatography of a partially degraded sample of the high molecular weight elastin allows the separation of tropoelastin (72,000 daltons) and a more acidic protein (65,000 daltons) which is distinct from tropoelastin yet contains hydroxyproline. The amino acid analysis of the two components added together yield a composition similar if not identical to proelastin.

Automated sequence analyses of the intact high molecular weight protein reveals an NH₂ terminal sequence homologous to tropoelastin. These data suggest that the 65,000 molecular weight protein is attached onto the C-terminals of tropoelastin.

The new model of elastin fibrogenesis is proposed based on initial alignment of proelastin molecules on the microfibril via disulfide linkages.