Purification and amino acid sequence of a noncalcitonin secretory peptide derived from preprocalcitonin

A previous report from this laboratory provided immunochemical and biochemical evidence for the existence of a secretory peptide derived from the noncalcitonin region of rat preprocalcitonin. By a variety of criteria, we demonstrated that this naturally occurring peptide was similar, if not identical, to a synthetic peptide which consisted of the NH₂-terminal 16 residues of the calcitonin mRNA translation product. We have now purified this peptide from rat medullary thyroid carcinoma and sequenced it. A rat tumor of the 1-2-4 tumor series was extracted in 0.1 N HCl yielding 900 μg of immunoreactive peptide. The peptide was purified to homogeneity by: trichloroacetic acid precipitation of contaminating protein; gel filtration; and finally, reverse phase high pressure liquid chromatography. Overall yield was approximately 24%. Amino acid analysis and sequencing of the peptide yielded a composition and sequence identical with that of the synthetic peptide.