Measurement of the absolute synthesis of soluble and insoluble elastin by chick aortic tissue.

The rate of in vitro synthesis of soluble and insoluble elastin by thoracic aorta of 2-day-old chicks has been measured in absolute terms. In the absence of beta-aminopropionitrile (beta APN), the steady state level of soluble elastin was 120 pmol/100 mg of aortic tissue or 3.7 micrograms/whole aorta segment. The rate of synthesis of elastin in vitro was approximately 130 micrograms/day per whole aorta segment. This is three- to four-fold lower than the estimated rate of in vivo synthesis for a comparable segment of aortic tissue at the same stage of development. Pulse-chase experiments suggested that this difference was not due to in vitro proteolysis of a significant proportion of the newly synthesized soluble elastin, but rather that the conversion of soluble to insoluble elastin was both rapid and efficient. These experiments also indicated the presence in aortic tissue of a substantial pool of elastin of intermediate solubility. Although inclusion of beta APN in the incubation medium resulted in an increase in the amount of soluble elastin in aortic tissue, the rate of accumulation of newly synthesized soluble elastin in the presence of this inhibitor of cross-linking was not linear, but decreased with incubation time. Furthermore, although beta APN effectively suppressed the appearance of insoluble elastin for at least 2 h, some escape from the effect of this inhibitor was seen with further incubation. In general, beta APN significantly depressed elastin synthesis.