Actinidin hydrolysis of substituted-phenyl hippurates: a quantitative structure-activity relationship and graphics comparison with hydrolysis by papain

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Abstract
The hydrolysis of 29 phenyl hippurates (XPhOCOCH2NHC(.dbd.O)C6H5) by the cysteine protease actinidin was studied and a quantitative structure-activity relationship (QSAR) was formulated: log 1/Km = 0.74.sigma. + 0.50.pi.''3 + 0.24MR4 + 2.90. In this expression .sigma. is the Hammett constant, .pi.''3 is the hydrophobic parameter for the more hydrophobic of the 2 m-substituents and MR4 is the molar refractivity of p-substituents. The QSAR for actinidin is compared with a similar one obtained for another cysteine plant protease papain. A color stereo computer graphics model constructed from the X-ray crystallographic coordinates of actinidin is compared with those of previously reported models for papain. [Thus, the study of enzyme-ligand interactions is one of the best ways to develop understanding of how drugs react with macromolecules.].