The subcellular distribution of peptides immunoreactive for the carboxyl-terminal extension of cholecystokinin in rat brain.

An antiserum raised against a synthetic peptide (D-10-Y) comprising the carboxyl-terminal extension of cholecystokinin (CCK) detects several immunoreactive peptides, which were found to be widely distributed in rat brain (1). This article reports the subcellular distribution of these D-10-Y-like immunoreactive peptides in whole rat brain. Primary subcellular fractionation yielded a mitochondrial (P2) and microsomal (P3) fraction, both of which were enriched in D-10-Y and CCK 8 peptide immunoreactivity. Further fractionation of P2 yielded a purified synaptosome fraction (P4) which was further enriched in D-10-Y and CCK 8-like peptides. Whole rat brain contains two major molecular forms of D-10-Y-like immunoreactivity, one similar in size to CCK 33 (peak 1) and one slightly larger than CCK 8 (peak 2). In the P2 and P3 fractions, most of the D-10-Y-like immunoreactivity was similar in size to peak 2. It is likely that this D-10-Y-like immunoreactive peptide is an intermediate in the processing of CCK 8, and its enrichment in nerve endings is consistent with the final cleavage and amidation reactions taking place in the nerve terminals.