The directed evolution of enantioselective enzymes (1 ,2 ) for use in organic synthesis constitutes an attractive alternative to traditional forms of asymmetric catalysis based on chiral transition metal complexes or catalytic antibodies. It involves the proper combination of molecular biological methods for random gene mutagenesis and gene expression coupled with appropriate high-throughput screening systems that allow the rapid determination of the enantiomeric purity of a chiral product. Typically, thousands of samples arising from the catalytic action of the evolved enzyme variants on a given substrate of interest need to be assayed within a reasonable time span, ideally within one day.
