Unusual four-bond secondary H/D isotope effect supports a short - strong hydrogen bond between phospholipase A(sub 2) and a transition state analogue inhibitor

A detailed analysis of prominent secondary four-bond hydrogen/deuterium isotope effect observed from proton NMR at the active site histidine imidazole ring of bovine pancreatic sPLA(sub 2) in the presence of a phosphonate transition state analogue is presented. Additional details are provided for the catalytic mechanism of sPLA(sub 2) and it is demonstrated that the intrinsic H/D secondary isotope effect is useful to hydrogen bond strength.