Isolation of a cross-linked dimer of elastin.

Salt-soluble elastin, isolated by coacervation from extracts of copper-deficient pig aorta, contains a minor protein component separable by gel electrophoresis in 6 M urea. This protein has a molecular weight of 150,000 compared to 75,000 of the major component. The amino acid analyses of both proteins are typical of elastin but the higher molecular weight component has a significantly lower lysine content and lysine-derived cross-links that are lacking from the major component. The proteins were labeled by incubation of the fresh aortic tissue with [14C]lysine. The acid hydrolysate of the borohydride-reduced higher molecular weight protein contained a labeled amino acid eluting at a time identical to standard merodesmosine and a trace of radioactivity corresponding to lysinonorleucine. We conclude that the higher molecular weight protein is a cross-linked dimer of the previously identified soluble elastin.