The role of the tryptophan residues in the activity of the nerve growth factor

The nerve growth factors isolated from mouse submaxillary glands and Naja naja venom have been treated with N-bromosuccinimide in buffer and in solutions of 8 M urea. The nerve growth factors thus oxidized at progressive numbers of tryptophan residues have been analyzed for their biological and immunological activities. The nerve growth factor from mouse submaxillary gland contained 6 reactive tryptophan residues, one of which was oxidized only in solutions of 8 M urea. The 4 tryptophan residues of Naja naja nerve growth factor, instead, were all readily oxidized in buffer at pH 4. Losses of biological and immunological activities were parallel. Whereas all 4 of the tryptophan residues of Naja naja nerve growth factor were necessary for full biological activity, only 4 of the 6 tryptophan residues found in mouse submaxillary gland nerve growth factor appeared to contribute to the biological and antigenic activities of the molecule.