The hydrolysis of a tetrapeptide, H-His-Ser-Asp-Ala-OH, corresponding to the N-terminal portion of vasoactive intestinal polypeptide (VIP) was examined. At pH 5.0, Ala was released at a much faster rate than His, while the release of His was predominant at pH 7.78. When examined by nuclear magnetic resonance spectroscopy, the pD dependence of chemical shift was especially pronounced at the His residue, but in a different manner from that observed in a His monomer. On the basis of calculation of rotamer population ratios, a relationship between the predominant G' conformation of the His residue and faster hydrolysis of the tetrapeptide at lower pH is postulated.
研究了与血管活性肠
多肽(VIP)N 末端部分相对应的四肽 H-His-Ser-Asp-Ala-OH 的
水解过程。在 pH 值为 5.0 时,Ala 的释放速度比 His 快得多,而在 pH 值为 7.78 时,His 的释放占主导地位。通过核磁共振波谱分析,
化学位移的 pD 依赖性在 His 残基处尤为明显,但与在 His 单体中观察到的方式不同。根据旋转体数量比的计算,推测 His 残基的 G'构象占优势与四肽在较低 pH 值下
水解速度较快有一定关系。