An HPLC and RIA analysis of the cholecystokinin peptides in rat brain

Methanol and boiling water extracts of rat brain were chromatographed on two HPLC columns and the major cholecystokinin (CCK) peptides that eluted were detected by radioimmunoassay. The major CCK-like substance in both extracts co-chromatographed with CCK octapeptide sulfate on both columns, in agreement with previous reports of gel filtration chromatography of extracts of rat (1), porcine (2), human (2), and guinea pig brain (3). Minor immunoreactive components were detected in both extracts which chromatographed with CCK8 desulfate, CCK4 or 5, and variable amounts of partially or completely oxidized CCK8 sulfate and desulfate. Little or no immunoreactivity comigrated with sulfated or desulfated gastrin 17.In boiling water extracts, two additional peaks of immunoreactivity were detected, one which co-elutes with CCK33 and one which precedes CCK33 and has an apparent molecular weight of 40,000–50,000. This “pro-CCK” is not dissociated by treatment with sodium dodecyl sulfate and is considerably less hydrophobic than CCK8 or CCK4. It may be the same as the putative CCK precursor reported by Rehfeld to incorporate ³⁵S methionine in rat cortex (4) which yields CCK8 upon trypsinization (5).