Abstract: Recombinant cells and an improved method utilizing them is disclosed for the preparation of an optically pure, L-amino acid from its D and D,L isomer forms. The process utilizes cell cultures that possess high aminotransferase activity that exhibits moderate selectivity in the conversion of D and L amino acids to their respective 2-keto acids as well as absolute stereospecificity in the conversion of the 2-keto acids to the L isomer alone.

Abstract: A method for the isolation of a substantially pure L-isomer of an amino acid from its D,L racemic mixture does not require the use of a resolving agent, the formation of a derivative of the amino acid or additional enzymic reactions.The method is based upon the concept of the equal saturation point wherein the L-isomer can be separated from the D-isomer by precipitation of the L-isomer when the relative concentration of the D-isomer is less than 7.0% or by precipitation of the D,L racemate when the relative concentration is greater than 7.0%. Selective crystallization through seeding allows for further isolation of pure L-isomer when its relative concentration in solution is very low.