Overexpression of the gene forN-acylamino acid racemase fromAmycolatopsis sp. TS-1-60 inEscherichia coli and continuous production of optically active methionine by a bioreactor

A DNA sequence encodingN-acylamino acid racemase (AAR) was inserted downstream from the T7 promoter in pET3c. The recombinant plasmid was introduced intoEscherichia coli MM194 lysogenized with a bacteriophage having a T7 RNA polymerase gene. The amount of AAR produced by theE. coli transformant was 1100-fold more than that produced byAmycolatopsis sp. TS-1-60, the DNA donor strain. The AAR was purified to homogeneity from the crude extract of theE. coli transformant by two steps: heat treatment and Butyl-Toyopearl column chromatography. Bioreactors for the production of optically active amino acids were constructed with DEAE-Toyopearl-immobilized AAR andd- orl-aminoacylase.d- orl-methionine was continuously produced with a high yield fromN-acetyl-dc-methionine by the bioreactor.