Organophosphate spin-label studies of inhibited esterases, α-chymotrypsin and cholinesterase

A new ESR spin-label has been synthesized which parallels the action of the standard DIFP (diisopropylfluorophosphate) inhibitors for esterase enzymes. The labels differ from DIFP in that one or more of the ester linkages is an organic nitroxide molecule. Preliminary inhibition studies of α-chymotrypsin, trypsin, choline-esterase, and thrombin show strikingly different spectra for the spin-labelled inhibited enzymes indicating a variation in the structure of the active site in the vicinity of the active serine. It is suggested that such labels should be of a very general use in studying the nature of the active site under catalytic conditions.