Isolation of a soluble protein resembling elastin

There are strong indications of a defect in elastogenesis in copper deficiency. This is manifested by histologic lesions of the elastic membranes. Furthermore, analysis of stretch moduli of copper deficient aortic rings indicate a marked decrease in tensile strength. Elastin isolated from copper deficient aortas has an increased solubility in formic acid and the amino acid composition of this elastin indicates a decrease in the cross-linking amino acids. The basis of the defective cross-linking is thought to be the failure of the oxidation and condensation of epsilon-amino groups of lysine residues preexisting in straight chain elastin precursors. An excess of unidentified salt soluble proteins in these aortas has suggest that a soluble elastin precursor may accumulate as a result of a block in the cross-linking reaction. The reversible coacervation of a cold soluble protein in this fraction upon warming and cooling has provided a means of partial purification of this protein. Aortas from copper deficient swine were extracted in buffered 1 M NaC1 solutions overnight as 4 degrees C. The salt extracts were filtered cold and the filtrate was further clarified by centrifuging at 100,000xg at 4 degrees C for 30 minutes. The filtrate was warmed to 23 degrees and the heat precipitable fraction was collected by centrifuging for 1 hour at 22,000xg. The precipitate was redissolved and reprecipitated twice more to obtain a clear solution. Disc electrophoresis indicated the presence of one major protein an amino acid analysis revealed that its composition was basically close to that of elastin. The high content of the amino acid and high content of lysine indicate that the soluble protein may be a precursor of insoluble elastin. The reversible heat precipitation shown by the soluble protein found in copper deficient aortas is also exhibited by alpha-elastin; a large soluble degradation product of insoluble elastin produced by partial hydrolysis. This unusual property of reversible heat precipitation at room temperature is not shown by any other protein.