The use of crystallography, graphics, and quantitative structure-activity relationships in the analysis of the papain hydrolysis of X-phenyl hippurates

The effect of 3- and 4-monosubstitution and 3,5-disubstitution on the phenyl leaving group of the papain-catalyzed hydrolysis of 27 phenyl hippurates is reported. The Michaelis-Menten constant ( K m ) at 25.0 °C and pH 6.0 was determined for the substrates and, in addition, the first-order rate constant ( k) for the uncatalyzed hydrolysis under the same conditions was measured. A quantitative structure-activity relationship was derived from the K m values. The conclusions from this analysis are in excellent agreement with the binding mode of the hippurates as shown by a molecular graphics analysis of the binding cavity which has been defined by X-ray crystallography.