Ultrasonic relaxation measurements for ~-chymotrypsin in phosphate, sulfite and arsenate buffers exhibit a high peak of absorption at neutral pH. The analysis is based on: (i) comparison of the relaxation measurements for the enzyme and for the zymogen and inhibited enzyme; (ii) X-ray and neutron diffraction data, and high-resolution NMR data. The ultrasonic relaxation is shown to result mainly from a proton-transfer reaction that involves the histidine at the catalytic site (His-57). The question is raised of whether the enhanced ultrasonic effect observed in the enzyme is indicative of a property that plays a part in the catalytic activity.

Deconvolution of ultrasonic data into single relaxations is rarely feasible when only the absorption or the velocity of the waves is measured. Here we use both series of data to construct a Cole-Cole diagram for a solution. When applied to alpha-chymotrypsin, this method shows two relaxations that are well separated on the time scale, a result that will help simplify analyses of the ultrasonic data for this enzyme.