Tachykinins (Substance P, Neurokinin A and Neuropeptide γ) and neurotensin from the intestine of the burmese python, python molurus

Peptides with substance P-like immunoreactivity, neurokinin A-like immunoreactivity and neurotensin-like immunoreactivity were isolated in pure form from an extract of the intestine of the Burmese python (Python molurus). The primary structure of python substance P (Arg-Pro-Arg-Pro-Gln-Gln-Phe- Tyr-Gly-Leu-Met-NH₂) shows one amino acid substitution (Phe⁸ → Tyr) compared with chicken/alligator substance P and an additional substitution (Lys³ → Arg) as compared with mammalian substance P. The neurokinin A-like immunoreactivity was separated into two components. Python neuropeptide γ (Asp-Ala-Gly-Tyr-Ser-Pro-Leu-Ser-His-Lys-Arg-His-Lys-Thr-Asp-Ser-Phe-Val- Gly-Leu-Met-NH₂ shows three substitutions (Gly⁵ → Ser, Gln⁶ → Pro and lle⁷ → Leu) compared with alligator neuropeptide γ and an additional substitution (His⁴ → Tyr) compared with mammalian neuropeptide γ. Python neurokinin A (His-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met. NH₂) is identical to human/chicken/alligator neurokinin A. Python neurotensin (pGlu-Leu-Val-His- Asn-Lys-Ala-Arg-Pro-Tyr-lle-Leu) is identical to chicken/alligator neurotensin. The data are indicative of differential evolutionary pressure to conserve the amino acid sequences of reptilian gastrointestinal peptides.