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

A previous report from this laboratory (Birnbaum R. S., O'Neil, J. A., Muszynski, M., Aron, D. C., and Roos, B. A. (1982) J. Biol. Chem. 257, 241-244) 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 micrograms of immunoreactive peptide. The peptide was purified to homogeneity by: 1) trichloroacetic acid precipitation of contaminating protein; 2) gel filtration; and finally, 3) 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.