Characterization of the Proα1 Chain of Procollagen

Radioactively labeled proα1 chains, obtained by culture of embryonic chick cranial bones in the presence of [35S]cysteine, were cleaved with cyanogen bromide. A 35S-containing peptide was isolated and purified by agarose and DEAE-cellulose chromatography. Its molecular weight, determined by sodium dodecyl sulfate acrylamide gel electrophoresis, was approximately 20,000. Labeling experiments with [3H]tryptophan revealed that the peptide also contained tryptophan. Comparison of the amino acid composition and molecular weights of purified proα1 and α1 chains indicated that the CNBr peptide contained the great majority of the additional sequence present in the precursor proα1 chain. The amino acid composition of this sequence clearly precludes its existence in a triple helical conformation.