Evidence that tropoelastin is the primary precursor in elastin biosynthesis.

2803) have presented evidence for the existence of a 120,000-to 130,000-dalton intermediate designated proelastin.This proelastin had a significant histidine content while tropoelastin, like elastin, does not contain histidine.Therefore, if proelastin is an intermediate, elastin biosynthesis might be affected by histidine analogs such as histidinol, but if only tropoelastin is an intermediate, it might be unaffected.Histidinol was shown to competitively inhibit histidinyl synthetase isolated from chick embryos, but it did not inhibit other synthetases.Incubation of 9-day chick aortae with increasing concentrations of histidinol progressively inhibited r3H]histidine incorporation into protein, reaching 82% inhibition at 20 mM.When the aortae were incubated with [3H]glycine under control conditions, 19% of the incorporated label was found in procollagen and 25% in tropoelastin as determined by polyacrylamide gel electrophoresis.In the presence of 20 m~ histidinol, only 9% of the r3H]glycine was found in procollagen while 50% was now in tropoelastin.Experiments using elastin-specific and collagen-specific antibodies confirmed the observation that collagen synthesis was markedly inhibited by histidinol while tropoelastin synthesis was relatively unaffected.Pulsechase experiments demonstrated that labeled tropoelastin was efficiently incorporated into insoluble elastin both in the presence and absence of histidinol.These results suggest that tropoelastin is the primary precursor in elastin biosynthesis in the chick aorta.