Libraries of transaminase mutants were generated by site saturation mutagenesis, targeting active site, 2 nd sphere and dimer interface amino acid residues or combinatorial libraries that randomly combined beneficial mutations found in a round. Saturation mutagenesis libraries were constructed by overlap extension PCR. The degenerate NNK codon was used to generate fragments that coded for all 20 amino acids. The linear fragments were then amplified using the appropriate 3' and 5' oligonucleotide primers The linear fragments and the pET28b vector were digested using Nde I and Xho I endonucleases, PCR purified and ligated using T4 DNA ligase. After each round of evolution, combinatorial libraries were generated by overlap extension PCR. Primers were designed that encoded either the parent amino acid or the identified mutation, These primers were used to generate short fragments which were gel-purified and mixed appropriately in overlap extension PCR to generate genes containing all possible combination of mutations. Genes were cloned as described above.