Conformation and Activity of Chymotrypsin: The pH-Dependent, Substrate-Induced Proton Uptake

Hydrogen ion uptake by chymotrypsin during reversible binding of specific substrate is shown to be due to an ionizing group of the enzyme with a pK (apparent) ∼9 in the free enzyme. This pK (apparent) is shifted to higher value in the enzyme-substrate complexes. Previous results indicating an equilibrium, controlled by this ionizing group, between active and inactive conformational forms of chymotrypsin are confirmed.