Immunogenic and antigenic properties of the COOH-terminal hexapeptide of substance P.

Substance P (SP) and its COOH-terminal fragment (6-11) were coupled to bovine serum albumin by glutaraldehyde and used to elicit antibodies. Anti-SP and anti-SP6-11 antibodies bound to the same extent 125I-[Tyr8]-SP and 125I-[T-Lys6]-SP6-11. The latter was obtained after conjugation of the [Lys6]-SP6-11 with cold Bolton-Hunter reagent and then labelling by the chloramine-T method. In contrast to 125I-[Tyr8]-SP, 125I-[Tyr8]-SP6-11 was poorly bound by both anti-SP and anti-SP6-11 antibodies. Synthetic fragments of SP shorter than SP7-11 did not react with anti-SP6-11 antibodies. It is concluded that the antigenic determinant is within the COOH-terminal pentapeptide, and that Phe7, Phe8, Leu10 and Met11 contribute significantly to both anti-SP and anti-SP6-11 immunoreactivity.