Specificity of antisera obtained to Substance P and its C-terminal hexapeptide

Synthetic fragments and analogs were used to characterize specificity of antisera toSP and SP_6–11. [Tyr⁸]SP and [Lys⁶]SP_6–11 were both used as radioiodinated ligands. The latter was conjugated with Bolton-Hunter reagents before labelling. In both systems, the C-terminal pentapeptide SP_7–11 was the shortest fragment showing antigenic identity with Substance P molecule. Substitution of different amino acid residues in SP_6–11 by His or Gly showed that all but Glu⁶ take part in the structure of the antigenic determinant.