A presumptive subunit of elastic fiber microfibrils secreted by arterial smooth-muscle cells in culture.

Monkey smooth cells, maintained for five weeks in confluent cultures, accumulated a substantial extracellular matrix. Elastic fibers possessing the characteristic amorphous elastin component and 11 nm diameter microfibrils could be isolated from this matrix by extraction with 5 M guanidine. Further extraction under reducing conditions selectively removed the microfibrillar component. Gel electrophoresis of this extract in the presence of sodium dodecylsulfate revealed a single protein band with an apparent molecular weight of 270000. The amino acid composition of this presumptive subunit of the microfibrillar protein was rich in acidic and hydrophilic amino acids and distinctly different from that of collagen or elastin. When smooth muscle cell cultures were incubated with labeled cystine, the predominant labeled protein in the culture medium also had a molecular weight of 270000. This labeled protein comigrated with a major protein band and could be partially purified by DEAE-cellulose ion-exchange chromatography and gel filtration on agarose. It shared manu of the properites of the presumptive microfibrillar protein.