Ultrasonic studies of proton-transfer reactions at the catalytic site of alpha-chymotrypsin.

Ultrasonic relaxation measurements for alpha-chymotrypsin in phosphate, sulfite and arsenate buffers exhibit a high peak of absorption at neutral pH. The analysis is based on: comparison of the relaxation measurements for the enzyme and for the zymogen and inhibited enzyme; 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.