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SIMILARITY AND DISSIMILARITY IN THE STEREOGEOMETRY OF THE ACTIVE SITES OF THROMBIN, TRYPSIN, PLASMIN AND GLANDULAR KALLIKREIN

The relationship between chemical modifications of arginine derivatives and inhibitory activity to trypsin, plasmin and glandular kallikrein was investigated comparing with that of thrombin and concluded as follows: The hydrophobic binding pocket, which has been reported previously to be stereogeometrically very similar in trypsin and thrombin, corresponded to the length of ethylpiperidine. Concerning the site (termed the P site) next to the hydrophobic binding pocket, there were large differences in stereogeometry between trypsin and thrombin; the binding site of trypsin extended further to allow propyl and phenyl group attached to piperidine, while that of thrombin would be much narrower and unable to allow them. The P sites of plasmin and glandular kallikrein resembled that of trypsin in being able to allow phenyl group. To substantialize the hydrophobic binding pocket and the P site, a (2R, 4R)-MQPA-trypsin complex model was generated using the results of X-ray crystallography of (2R, 4R)-MQPA and BPTI-trypsin complex by calculation to minimize van der Waals contacts, and it was of great use for understanding the geometry of the active sites of trypsin, thrombin, plasmin and glandular kallikrein.