Turnover numbers (0.032-0.008 min-1) of purified mutants Lys94-Glu, Lys99-Glu, Lys105-Glu, Lys440-Glu, Lys453-Glu, Arg455-Glu, and Lys463-Glu toward 7-ethoxycoumarin were much lower than that (0.380 min-1) of the wild type at 25 degrees C.