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.
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