Purified .beta.-amino acids are of considerable interest in the preparation of pharmacologically active compounds and industrial precursors. Although enantiomerically pure .beta.-amino acids can be produced by standard chemical synthesis, this traditional approach is time consuming, requires expensive starting materials, and results in a racemic mixture which must be purified further. However, DNA molecules encoding lysine 2,3-aminomutase can be used to prepare .beta.-amino acids by methods that avoid the pitfalls of chemical synthesis. The present invention provides a method of producing enantiomerically pure .beta.-amino acids from .alpha.-amino acids comprising catalyzing the conversion of an .alpha.-amino acid to a corresponding .beta.-amino acid by utilizing a lysine 2,3-aminomutase as the catalyst.