SUBSTANCE-P INACTIVATION BY TRANSGLUTAMINASE INVITRO

Gamma(glutamyl5)spermine derivative of substance P (Spm-SP) was synthe sized in vitro in the presence of purified guinea pig liver transgluta minase and Ca2+. The spermine adduct of the neuropeptide was purified by HPLC on a reversed-phase column and characterized by fast atom bomb ardment mass spectrometry. The biological activities of Spm-SP were te sted by assaying, in comparison with substance P, its ability to induc e both the contractions of smooth muscle in vitro and the edema format ion in vivo. Spm-SP was shown not to elicit contractile responses in t he isolated rat stomach strip and duodenum and not to antagonize the s pasmogenic effect evoked by the native neuropeptide. Furthermore, Spm- SP was unable, when administered into rats by plantar injection, eithe r to provoke an acute inflammatory response in the hind limb or to ant agonize the edema formation induced by a concurrent administration of substance P. These results indicate that the introduction of a large s ize hydrophilic moiety at the glutamine' level negatively affects the ability of the neuropeptide to bind to its receptor(s), thus supportin g the view that the hydrophobic middle portion of substance P plays a kev role in receptor recognition.