Relevance of aggregation properties of tropoelastin to the assembly and structure of elastic fibers.

Solutions of tropoelastin incubated under different experimental conditions were examined by electron microscopy after negative staining and after fixation and embedding. Below 37 degrees C only polymorphous structureless elements of variable size could be found. In samples kept for a few minutes at 40 degrees C, flexible, isolated filaments of 5 nm diameter and variable length, together with a few small aggregates of filaments, were seen. No single filaments, but only bundles of filaments were detectable after incubation at 40 degrees C for longer than 5-10 min. Tropoelastin kept at 40 degrees C for longer than 10 hr formed a white precipitate, which, when fixed and embedded as in conventional electron microscopy, consisted of 0.5-2 microns thick, amorphous and branching fibers, identical to those seen in identically processed normal tissues. From these observations a model for the assembly and structure of elastic fibers is proposed.