Mutagenized libraries for screening studies were generated by error-prone PCR using the GeneMorph II Random Mutagenesis kit (Agilent) and transformed into E. coli Bl21 (DE3) and individual colonies picked and grown in 96-well plates. The Kemp eliminase activity of ~600 variants were assayed with 5-nitrobenzisoxazole (0.25 mM) in 96-well plates. This primary screening served to select variants that were subsequently prepared and tested on pure form. In most cases, this secondary screening implied the determination of profiles of activity versus substrate concentration.