Molecular Forms of Katacalcin, Calcitonin Gene-related Peptide and Gastrin-releasing Peptide, in a Human Medullary Thyroid Carcinoma¹

Peptides synthesized by a human medullary thyroid carcinoma were purified to homogeneity by reverse-phase high performance liquid chromatography and structurally characterized by determination of amino acid composition, amino acid sequence, and fast atom bombardment mass spectra. The katacalcin-related material in the tumor extract was heterogeneous. Katacalcin (1–21) represented the predominant molecular form but metabolites, identified as katacalcin (1–20), (1–19), (1–15) and (1–13), were also identified in high concentration. Calcitonin gene-related peptide-I was isolated from the tumor but calcitonin gene-related peptide-II was absent. A minor component of calcitonin gene-related peptide-like immunoreactivity was of higher molecular weight and may represent an incompletely processed form of the prohormone. Gastrin-releasing peptide (1–27) and gastrin-releasing peptide (18–27) (neuromedin C) were isolated from the tumor but gastrin-releasing peptide (14–27) and bombesin were absent.