The reaction of p-nitrophenyl esters with chymotrypsin and insulin.

was discussed. This compound is a member of a group of organophosphorus insecticides which are powerful inhibitors of cholinesterases. They will also inhibit chymotrypsin, and it has been shown that this inhibition is due to combination of the compounds with a single active centre in the enzyme (Jansen, Nutting & Balls, 1949; Hartley & Kilby, 1952).We investigated the reaction ofchymotrypsin with certain structural analogues of E 600, namely p-nitrophenyl ethyl carbonate (NPC)