Apparent Autolysis of the N-Terminal Tetrapeptide of Vasoactive Intesinal polypeptide (VIP)

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.