Immunochemical analysis of substance P using its synthetic fragments and analogs.

Synthetic fragments and analogs were used to characterize specificity of antisera to substance P. Both, the C-terminal hexapeptide and the pentapeptide completely inhibited binding of 125I-[Tyr8]substance P by these antisera, showing the antigenic identity with substance P. Synthetic fragments shorter than peptide (7-11) did not react with anti-substance P antisera in this system. Substitution of amino acids in different positions in the fragments (6-11) or (7-11) by histidine or glycine revealed that all five amino-acid residues take part in a structure of the antigenic determinant.