Photochemistry of enzyme-bound cinnamoyl derivatives

p-(Diethylamino)-o-hydroxy-α-methylcinnamoyl (CINN) was used as an acylating moiety for the formation of stable CINN-enzymes at the active site serine residues of the enzymes chymotrypsin, Factor Xa, and thrombin. Photolysis of the stable CINN-enzymes generates enzymatic activity via the proposed consecutive steps of photoisomerization (rate-determining step) and thermal lactonization (fast). Photochemical studies were undertaken to assess how an enzyme active site could alter the photochemistry ot the cinnamoyl derivative. Quantum yields for E to Z photoisomerization (Φ E→Z ) were measured for the three CINN-enzymes at 366 nm (20 o C in pH 7.4 Tris buffer) and tor the model system ethyl p-(diethylamino)-o-hydroxy-α-methylcinnamate (CINN-OEt)