Cleavage of substance P to an N-terminal tetrapeptide and a C-terminal heptapeptide by a post-proline cleaving enzyme from bovine brain

A post-proline cleaving enzyme isolated from bovine brain and previously shown to act on the neuropeptides thyrotropin releasing hormone (TRH: pGlu-His-Pro-NH₂) and luteinizing hormone releasing hormone (LRH: pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH₂) has now been found to cleave the Pro⁴-Gln⁵ bond in substance P (SP: H-Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂) to yield the N-terminal tetrapeptide H-Arg-Pro-Lys-Pro-OH and the C-terminal heptapeptide H-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂. The site of cleavage of the undecapeptide was confirmed by chemical synthesis of SP peptide fragments, by high performance liquid chromatographic analysis, and by high-voltage paper electrophoresis, thin layer chromatography and amino acid analysis. In addition, SP was shown by enzyme kinetic analysis to act as a potent competitive inhibitor of the enzymatic hydrolysis of the synthetic post-proline cleaving enzyme substrate carbobenzoxy-Gly-Pro-para-nitroanilide. It is known that the heptapeptide is as active as SP itself in a variety of bioassays, whereas the tetrapeptide has been reported to induced cyclic AMP formation and neurite extension in neuroblastoma cells and to enehance the phagocytosis activity of macrophages. These observations suggest that SP may play a dual role, with one activity residing in its C-terminal part, and the other in the N-terminal part of the molecule.