Reaction of a Specific Tyrosine Residue of Papain with Diisopropylfluorophosphate

Diisopropylfluorophosphate reacts with mercuripapain, 2,3-dimercaptopropanol-activated mercuripapain, and unactivated native papain with the incorporation of a maximum of 1 mole of phosphate per mole of protein. This alkylphosphorylation does not inhibit the potential activity of mercuripapain but does result in about 50% inhibition of 2,3-dimercaptopropanol-activated mercuripapain. The stoichiometric reactions of diisopropyl-1,3-14C-fluorophosphate and 32P-diisopropylfluorophosphate, respectively, with native and mercuripapain both occur at tyrosyl residue 123, with the formation of an O-diisopropylphosphoryl-l-tyrosyl residue.