Biosynthesis of tachykinins (substance P, neurokinin A and neuropeptide K) in neurons of the guinea pig myenteric plexus.

Incubation of the myenteric plexus-containing longitudinal muscle layer of guinea pig small intestine with [(35)S]methionine for up to 9 h resulted in a progressive increase in the incorporation of radioactivity into newly synthesized substance P, neurokinin A and neuropeptide K. The radiolabelled peptides were isolated from tissue extracts by immunoprecipitation using regionally-specific antisera and purified by reverse-phase high performance liquid chromatography. Incorporation of radioactivity into the tachykinins was abolished by cycloheximide and was not observed when [(35)S]cysteine was substituted for [(35)S]methionine. The method may be used to study the regulation of biosynthesis and posttranslational modification of protachykinins in the gut.