Antigenic sites on mouse 2.5S nerve growth factor

Cyanogen bromide and tryptic peptides of mouse 2.5S Nerve Growth Factor (NGF) have been used to inhibit competitively binding of rabbit antiserum anti-NGF to native NGF in a solid-phase radioimmunoassay. The results showed that the larger of the two peptides obtained by cyanogen bromide cleavage (amino-acid residues 10-118) was indistinguishable from NGF in this respect, whereas the smaller N-terminal peptide (residues 1-9) was virtually non-inhibitory. Ten peptides were purified from a tryptic digest of the larger cyanogen bromide fragment. One of them, peptide G7 (residues 58-59, 60-69, 104-114, linked by disulfide bridges), was capable of almost full inhibition of binding, though only when used at a concentration about 100 times higher than that necessary to get the same effect with NGF. One other peptide, G10-H1 (residues 70-74), showed some inhibition at relatively high concentrations, but the majority of peptides, including peptide DE-5 which has been shown to be active in the NGF bioassay, were essentially non-inhibitory. A significant co-operative effect was seen when peptides G7 and G10-H1 were used in conjunction. No such effects were observed with any other combination tested.