Hinge-bending deformation of enzyme observed by microwave dielectric measurement

A dielectric relaxation peak due to an intramolecular motion in the active site of trypsin was first observed in aqueous solution below the freezing temperature of bulk water by a time domain reflectometry method. If trypsin inhibitor is added to the solution, it vanishes. It is suggested that the motion observed is a hinge-bending deformation giving rise to the enzymatic activity of trypsin, which is prohibited by linkage of the trypsin inhibitor. Relaxation time of the motion is 3 × 102 ns at − 10°C.