Ultrastructural aspects of freeze-fractured and etched elastin.

The ultrastructural organization of fresh and purified elastin from beef ligamentum nuchae was studied by means of the freeze-etching technique. Both fresh and purified elastin showed a regular three-dimensional network of filaments which seemed to he composed of a sequence of globular subunities. There were also areas, along the regular network, in which ridges of various lengths, packed with perpendicular side filaments, were visible. In replicas of deep-etched and rotary-shadowed specimens, a thicker and more defined three-dimensional network was observable. A great variability in appearance among the globular subunits of the filaments was noticed which was at least partially due to the etching treatment. By means of computerized simulation of replicas of various hypothetically collapsed globular structures, we obtained patterns which were superimposable on those obtained in the replicas of the specimens analyzed. It is thus assumed that each globular subunit of the filament, being subjected to collapsing, has a less dense central core.