Generation of [Ala¹, Thr⁶]Bradykinin in the Plasma of a Snake, the Reticulated Python

Incubation of heat-denatured plasma from the reticulated python, Python reticulatus with trypsin generated bradykinin-like immunoreactivity which was detected by radioimmunoassay using an antiserum raised against mammalian bradykinin. The primary structure of python bradykinin was established as Ala-Pro-Pre-Gly-Phe-Thr-Pro-Phe-Arg. This amino acid sequence contains two substitutions (Arg¹ → Ala and Ser⁶ → Thr) compared with mammalian bradykinin. Treatment of python plasma with glass beads under conditions previously shown to generate [Thr⁶]bradykinin in the plasma of a turtle and an alligator did not generate bradykinin-like immunoreactivity. The data indicate that the plasma of a lepidosaur contains a kininogen but, unlike the plasma of chelonians and crocodilians, does not contain a prekallikrein activator related to Factor XII.