Two shorter peptides of a heat-stable enterotoxin (STp), which is produced by enterotoxigenic Escherichia coli strain 18D, were prepared by two different procedures; i) chemical synthesis and ii) Edman-degradation of STp. These peptides (designated as STp(4–18) and STp(5–18)) corresponded to 15 and 14 amino acid residues in the sequence of STp without three and four residues, respectively, of the N-terminus. Peptides STp(4–18) and STp(5–18) prepared by chemical synthesis had the same biological and physicochemical properties as the peptides obtained by the Edman method. Furthermore, they showed almost the same toxicity as native and synthetic STp, and their toxicity was neutralized by anti-native STp antisera. Synthetic STp(4–18) had similar heat-stability to STp, but synthetic STp(5–18) was much more heat-stable. These findings suggest that the sequence from the Cys residue near the N-terminus to the C-terminal residue is extremely important for the unique characters of toxicity and heat-stability of the toxin.
通过两种不同的方法制备了热稳定肠毒素(STp)的两个短肽,STp 是由肠毒性大肠埃希氏菌株 18D 产生的。这些肽(命名为 STp(4-18) 和 STp(5-18))分别对应于 STp 序列中的 15 和 14 个
氨基酸残基,N-端分别缺失 3 和 4 个残基。用
化学合成法制备的肽 STp(4-18) 和 STp(5-18) 与用埃德曼法制备的肽具有相同的
生物学和理化性质。此外,它们与原生 STp 和合成 STp 表现出几乎相同的毒性,并且它们的毒性可被抗原生 STp 抗血清中和。合成 STp(4-18) 的热稳定性与 STp 相似,但合成 STp(5-18) 的热稳定性更强。这些研究结果表明,从靠近 N 端的 Cys 残基到 C 端残基的序列对毒素的毒性和热稳定性的独特性极为重要。