Chang L S, Kuo K W, Chang C C
Department of Biochemistry, Kaohsiung Medical College, Taiwan, ROC.
Biochem Mol Biol Int. 1993 Mar;29(3):435-42.
Acrylamide quenching studies indicated that the exposure degree of the Trp residue in cobrotoxin was higher than that in alpha-bungarotoxin. The Trp residue of cobrotoxin was in a positively charged environment as revealed by iodide quenching, while the Trp residue of alpha-bungarotoxin was not accessible for iodide. Analysis of hydrophilicity profile and local concentration of positively charged residues of toxin molecule also indicated that Trp in cobrotoxin was in a highly hydrophilic and positively charged environment. Measurement of Trp fluorescence with increasing temperature showed that the stability of environment of Trp in alpha-bungarotoxin was higher than in cobrotoxin. Result of competitive binding for nicotinic acetylcholine receptor (AchR) between cobrotoxin and alpha-bungarotoxin revealed that the molecular interaction of the two toxins with AchR was not the same. These, together with the fact that the cationic groups of the two toxins are involved in the binding with AchR, suggest that the observed different environment surrounded Trp residue and different AchR binding mechanism might fulfill a different requirement of the invariant Trp in the lethality of cobrotoxin and alpha-bungarotoxin.
丙烯酰胺猝灭研究表明，眼镜蛇毒素中色氨酸残基的暴露程度高于α-银环蛇毒素。碘化物猝灭显示，眼镜蛇毒素的色氨酸残基处于带正电的环境中，而α-银环蛇毒素的色氨酸残基无法与碘化物接触。对毒素分子亲水性图谱和带正电残基局部浓度的分析也表明，眼镜蛇毒素中的色氨酸处于高度亲水且带正电的环境中。随着温度升高对色氨酸荧光的测量表明，α-银环蛇毒素中色氨酸环境的稳定性高于眼镜蛇毒素。眼镜蛇毒素和α-银环蛇毒素对烟碱型乙酰胆碱受体（AchR）的竞争性结合结果表明，两种毒素与AchR的分子相互作用不同。这些结果，再加上两种毒素的阳离子基团都参与与AchR结合这一事实，表明所观察到的色氨酸残基周围不同环境以及不同的AchR结合机制，可能满足了眼镜蛇毒素和α-银环蛇毒素致死性中不变色氨酸的不同需求。
