The recently reported amino acid sequence of preprocalcitonin predicted from cDNA analysis indicates that the 32-amino acid form of calcitonin is internally situated. Extending beyond the carboxyl-terminal proline of calcitonin is a 20-amino acid segment which contains the tetrapeptide Gly-Lys-Lys-Arg linking calcitonin to the remaining 16 amino acids. This same short segment separates the sequence of the amidated peptide melanocyte-stimulating hormone from corticotropin-like intermediate lobe peptide in mammalian corticotropins. The terminal hexadecapeptide sequence of preprocalcitonin (termed carboxyl-adjacent peptide, CAP, for its position relative to calcitonin) has been synthesized to establish a radioimmunoassay for an investigation of cross-reacting peptides in extracts of normal and neoplastic calcitonin-producing tissues. Gel filtration chromatography of a rat thyroid extract revealed a major peak of immunoreactive peptide of approximately the same molecular weight as synthetic CAP. A minor peak of higher molecular weight immunoreactive material was also observed. The isolelectric point of both the thyroid peptide and synthetic material was about 5.2. Immunoreactive CAP and calcitonin were found in approximately equimolar amounts in normal thyroid and in anaplastic and well differentiated rat medullary thyroid carcinomas. Immunoreactive CAP was not detected in any tissue which did not contain calcitonin. Monolayer cultures of a rat medullary thyroid carcinoma contained and secreted equimolar amounts of immunoreactive CAP and calcitonin under basal (1 mM Ca2+) and stimulated (4 mM Ca2+ and 1 μM glucagon) conditions. These data indicate that the thyroidal peptide is probably the hexadecapeptide CAP which is derived from the same translation product as calcitonin. The similarity between the processing of precursors to the amidated peptide melanocyte-stimulating hormone and the corticotropin-like intermediate lobe peptide and processing of calcitonin and CAP suggests that the sequence Gly-Lys-Lys-Arg is one amidation codon in mammalian systems.
|Original language||English (US)|
|Number of pages||4|
|Journal||Journal of Biological Chemistry|
|State||Published - 1982|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology