In vivo biosynthesis of cholecystokinin in hog cerebral cortex.
The biosynthesis of cholecystokinin (CCK) in the cerebral cortex of hogs was studied by intracisternal injections of [32S]methionine. At different times (15, 60 and 120 min) after the injection, cortex was isolated and extracted with boiling water and 0.5 M acetic acid. CCK in the extracts was immunosorbed, using an antiserum specific for the COOH-terminal sequence of CCK. Subsequently, the CCK-immunoreactivity was applied to Sephadex G-50 superfine columns. The fractionation showed incorporation in five molecular forms with elution constants of 0.08, 0.50, 0.90. 1.1 and 1.3. After a pulse period of 15 min, [32S]methionine was incorporated mainly into the largest form of CCK (Kav of 0.08). The incorporation in all forms increased during the first hour. After 2 hours, a decline occurred in the larger forms, whereas the incorporation in the octapeptide form and tetrapeptide-like form increased.