New fluorogenic substrate for esterase activity of alpha-chymotrypsin and related enzymes

A new fluorogenic substrate, benzyloxycarbonyl-L-phenylalanine 4-methylcoumaryl-7-ester, has been developed for determination of the esterase activity of alpha-chymotrypsin and related enzymes. Synthesis of the substrate was achieved simply by the carbodiimide condensation of benzyloxycarbonyl-L-phenylalanine and 7-hydroxy-4-methylcoumarin in a 86% yield. The esterase activity was measured by increase of the fluorescence intensity at excitation and emission wavelengths of 325 and 465 nm, respectively. An initial rate of hydrolysis was linear over a 100-fold range of the enzyme concentration. As little as 2 ng of alpha-chymotrypsin could be detected in the standard assay. A typical enzyme assay, stability of the substrate, kinetic parameters, and specific activity have been reported.