Rat sensory ganglia incorporate radiolabelled amino acids into substance K (neurokinin alpha) in vitro.

Isolated rat dorsal root ganglia incorporated [3H]valine, [3H]serine, [3H]phenylalanine and [3H]histidine into a peptide which co-eluted with authentic substance K (neurokinin alpha) on reverse-phase HPLC. Confirmation of the identity of this peptide with substance K was obtained by demonstrating that the sulphoxide derivative of the peptide co-eluted with substance K sulphoxide. Substance P and substance K were synthesised in the ratio 2.6:1. The implications of these results for the co-synthesis of substance P and substance K in sensory neurones are discussed.