Presence of elastin-related 45-kDa fragment in culture medium: specific cleavage product of tropoelastin in vascular smooth muscle cell culture.

Significant amount of 45-kDa polypeptide was found to be present in the cultured medium of chick aortic smooth muscle cells. The polypeptide as well as tropoelastin (65-kDa) reacted with monoclonal antibody for tropoelastin. Pulse-chase experiments revealed that the relative density of the 45-kDa polypeptide to tropoelastin increased with chase periods. Partially purified radioactive tropoelastin (65-kDa) was converted to a 45-kDa polypeptide fragment in the test tube. The processing from the 65- to the 45-kDa polypeptide in the test tube was inhibited by ethylenediaminetetraacetic acid but not by N-ethylmaleimide and aminophenylmethylsulfonyl fluoride. These results indicate that the 45-kDa fragment is a degradation product of tropoelastin and that processing is mediated by enzymatic cleavages with metal proteinase. Fully hydroxylated tropoelastin treated with ascorbic acid was more resistant to the enzymes than underhydroxylated tropoelastin with scorbutic condition, suggesting that the structural stability of tropoelastin is also involved in the processing rate.