The microfibrillar components of porcine lung elastic fiber.

Lung elastic fiber was isolated from anatomically defined porcine parenchymal tissue. Constituent microfibrillar acidic structural glycoproteins (external and meso) were obtained by mild dissociative quantitative procedures, leaving the elastin-rich fraction as the insoluble residue. The presumptive cross-link lysylnorleucine was identified in both of the highly aggregated acidic structural glycoprotein fractions. The external-acidic structural glycoproteins require dithiothreitol but not sodium dodecyl sulfate for solubility. Both sodium dodecyl sulfate and dithiothreitol at 55 degrees C are required to release meso-acidic structural glycoproteins from the elastic fiber. On the basis of physical characteristics, I propose a new fraction from elastic fiber, the meso-acidic structural glycoprotein. The meso-acidic structural glycoproteins may have been in longest and closest contact with the elastin core of the elastic fiber. Alkali-soluble peptides from the elastin-rich fraction contained desmosine and high concentrations of hydroxyproline, polar amino acids and lysylnorleucine. The cross-link, lysylnorleucine, may be evidence of covalent bonding of glycoprotein to elastin, explaining my inability to obtain the biopolymer elastin with the composition of tropoelastin corrected for the desmosine-lysine content.