Measurement and partial characterization of the C-terminal flanking peptides from bovine preprotachykinins in extracts of brain and gut

Sequence analysis of bovine cDNAs has shown that the biosynthetic precursors of the tachykinins (α-, β- and γ-preprotachykinins) contain a common amino acid sequence [AYERSVMQDYERRRK] in the C-terminal flanking region. Using an antiserum raised against the synthetic peptide [YERSVMQDYE] in a specific radioimmunoassay, preprotachykinin C-terminal flanking peptide (C-PPT)-like immunoreactivity was measured in extracts of bovine corpus striatum, cerebral cortex and small intestine in concentrations that were equimolar with substance P. Consistent with the presence of two amino acid substitutions in the C-terminal flanking region of human and rat preprotachykinins, the antiserum did not detect immunoreactivity in extracts of human and rat tissues. Chromatographic analysis of the extracts identified two major immunoreactive components. It is proposed that they represent the 16-amino acid residue C-terminal flanking peptide derived from β- and γ-preprotachykinins and the 37-amino acid residue C-terminal flanking peptide derived from α-preprotachykinin. Treatment of tissue extracts with carboxypeptidase B did not result in a change in C-PPT-like immunoreactivity or in a change in chromatographic properties of the C-terminal flanking peptides suggesting that the C-terminal basic tetrapeptide (RRRK) had already been removed from the primary transcript of the preprotachykinin mRNAs by the action of endogenous processing enzymes.