The rate-limiting step for hydrolysis of thepositivelycharged oxoester benzoylcholine (BzCh) by human butyrylcho linesterase (BuChE) is deacylation (k3 ), whereas it is acyla-tion (k2 ) for hydrolysis of the homologous thioester ben-zoylthiocholine (BzSCh). Steady-state hydrolysis of BzCh and BzSCh by wild-type BuChEand its peripheral anionic site mutant D70G was investigated at different hydrostatic pressures, which allowed determination of volume changes associated with substrate binding, and the activation vol-umes for the chemical steps
