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

The hydrolysis of 29 phenyl hippurates (XPhOCOCH2NHC(=O)C6H5) by the cysteine protease actinidin has been studied and a quantitative structure-activity relationship (QSAR) has been formulated: log 1/Km = 0.74 sigma + 0.50 pi'3 + 0.24MR4 + 2.90. In this expression Km is the Michaelis constant, sigma is the Hammett constant, pi'3 is the hydrophobic parameter for the more hydrophobic of the two meta substituents, and MR4 is the molar refractivity of para 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 our previously reported models for papain.