A radioimmunoassay of human
pancreastatin was developed using a rabbit antiserum that selectively recognized the C-terminal amidated end of the
peptide, and it was used for the identification of the molecular forms of
pancreastatin in human gut (stomach, duodenum, small intestine, colon) and endocrine
tumor extracts (liver metastasis of a
gastrinoma and a
medullary carcinoma of thyroid, one nonsecreting pancreatic
tumor, one recurrence of a gut
carcinoid, one
vipoma and one
insulinoma). In all gut extracts, a gel filtration chromatography revealed the presence of three peaks of
pancreastatin-like immunoreactivity. The predominant form eluted with an apparent molecular weight higher than that of
pancreastatin. This form was also predominant in the endocrine
tumors analyzed, except in the
insulinoma, where a lower molecular weight form predominated. The high molecular form was further purified from a liver
metastasis of a
gastrinoma. The
pancreastatin-like immunoreactivity eluted in all the chromatographical systems (reverse-phase, ion exchange) as a single peak that was finally purified to homogeneity and sequenced. The sequence of the first 29 N-terminal
amino acids was obtained unambiguously and corresponded to the sequence 210-238 of
chromogranin A. Considering the selectivity of the assay used for
peptide identification, this major form was identified as the fragment 210-301 of
chromogranin A. It is likely that the predominant form of
pancreastatin in human gut extracts and noninsular
tumors is a 92
amino acid peptide.