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The specificity and mechanism of pepsin action.

Publisher Summary This chapter discusses the specificity and mechanism of pepsin action. The chapter presents an experiment in which synthetic substrates whose structure could be varied systematically, whose solubility in aqueous media in the pH range 1–5 was sufficiently great to obviate the need to add organic solvents, and whose rate of hydrolysis by pepsin was considerably greater than that of the acyl dipeptide substrates. The presence of carboxyl groups in substrates was also avoided, because the pKa of these groups falls in the pH range of pepsin activity. The first substrate that met these criteria was Z-His-Phe-Phe-OEt; the presence of the charged imidazolium group confers moderate solubility on this compound in aqueous buffered solutions over the pH range 1–5, and this group is almost entirely protonated at these pH values.