The deacylation mechanism (Scheme 1) is now widely accepted . The deacylating water (DW) plays a crucial role in the reaction by attacking the carbonyl carbon of the acyl-enzyme, assisted by abstraction of a proton by Glu166 . Formation of the tetrahedral intermediate (TI) (Scheme 1B) is thought to be rate-limiting in deacylation . This is followed by proton transfers