J. Biol. Chem., Vol. 255, Issue 24, 11625-11628, Dec, 1980
In vitro biosynthesis of somatostatin. Evidence for two distinct preprosomatostatin molecules
D Shields
mRNA isolated from angler fish islets of Langerhans was translated in the
wheat germ cell-free protein-synthesizing system and the products
identified by immunoprecipitation with specific antibodies to somatostatin
followed by sodium dodecyl sulfate gel electrophoresis. As previously shown
(Shields, d. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 4074), a major
polypeptide of 18,000 dalton, designated preprosomatostatin, was
immunoprecipitable. Here, evidence is presented for an additional
somatostatin-immunoreactive polypeptide of apparent Mr = 19,000. The 19
kilodalton polypeptide was similar, but not identical with the 18
kilodalton preprosomatostatin, as determined by tryptic peptide analysis.
Comparison of the tryptic peptides of the 19,000 dalton polypeptide with
those of unlabeled somatostatin demonstrated that it contained the
authentic somatostatin sequence. Like the 18,000 dalton precursor, the
19,000 dalton polypeptide had the mature somatostatin sequence located at
its COOH terminus; it is proposed that this molecule is a minor species of
preprosomatostatin.