Elastin: Locus and Characteristics of Chromophore and Fluorophore

Abstract

Elastin, the main component of elastic tissue and ligament, is a yellow, insoluble, elastic protein exhibiting brilliant ultraviolet induced fluorescence in the visible region of the spectrum. Neither the color nor fluorescence can be explained by the presently documented amino acid composition, or by theories of secondary structure. Both the chromophore and fluorophore are degraded by conventional acid hydrolysis but may be freed, intact, from peptide linkage only by acid hydrolysis carried out under reducing conditions. That the chromophore or fluorophore are not related to the desniosines, as previously reported, is demonstrated by their rapid adsorption from a hydrolyzate onto charcoal, when the desmosines remain in the colorless non-fluorescent supernatant. In the free state the chromophore and fluorophore behave as easily oxidizable ampholytes possessing aromatic character. They are not readily eluted from polystyrene based ion exchangers.Elastin was digested with elastase and pronase to give 65 % hydrolysis, and theproductssubjected togel pernieation chromatography on Bio-Gel P2. Both the chromophore and fluorophore were eluted, together with the desniosines, entirely within the exclusion volume, in residues comprising 35% of the protein molecule. Since these residues represent the enzyme resistant regions of the protein, the locus of the chromophore and fluorophore indicates that they might be involved in covalent cross-linking. A previously reported fluorescent fatty acid is now known to be a Contaminant, not easily removed from the protein when purified by commonly used procedures. A survey is presented of the relative contribution of various crosslinking species, and other components, to the spectral properties of elastin.