台湾コブラ蛇毒の化学的研究 (第5報)

精製神経毒Neurotoxinの活性基に就いて

抄録

Kinetics of the deamination reaction of glycine with nitrous acid was examined and it was confirmed, as did the experimental results of Spero and Schantz, that it is a first-order reaction in the presence of an excess of sodium nitrite. In the case of neurotoxin, application of nitric acid, under the same conditions as for glycine, was found to effect inactivation whose rate progressed by the first-order reaction and at a fast rate. Its half-life is 41.5 minutes at pH 4.0 and 0°C, and 48.5 minutes at pH 4.45 and 0°C. As a result of comparison with deamination reaction of glycine and with past literature, inactivation of neurotoxin by nitrous acid is due to deamination. It is therefore concluded that the essential group responsible for the toxicity of neurotoxin is the amino group. The amino groups present in neurotoxin are that of N-terminal leucine and the ε-amino group of lysine in the peptide chain. Since ε-amino group of lysine is less reactive to nitrous acid than the α-amino group, the essential group responsible for the neurotoxin activity must be the amino group in N-terminal leucine.