The dominant role of amide group at C-terminus for recognition by antibody in primates against gonadotropin releasing hormone.

A monkey and a baboon immunized with GnRH-tetanus toxoid conjugate developed high anti-GnRH antibody titres which resulted in disruption of cyclicity and low estradiol and progesterone levels indicative of the inhibition of follicular development and ovulation. Sera of both animals reacted with GnRH(NH2) but were devoid of reactivity with peptide sequences, 4-6, 7-10 and 4-10 of GnRH as well as GnRH free acid. Both sera were however reactive with GnRH-Lys-muramyl dipeptide analogue and GnRH-Ala-Ala-Thr-Lys-Pro-Arg-OH. As these compounds differ from GnRH-free acid by the presence of amide linkage at C-terminus of GnRH, these studies point to the importance of the conformation involving amide group at this position for immunoreactivity.