High-level expression of Trigonopsis variabilis D-amino acid oxidase in Escherichia coli using lactose as inducer

The use of lactose as inducer for the expression of Trigonopsis variabilis D-amino acid oxidase gene (daao) was investigated in Escherichia coli regul ated by T7 or T5 promoter. The daao gene was prepared by reverse transcript ase-polymerase chain reaction and cloned into pET21b and pQE-30 to yield pE T-DAAO and pQE-DAAO, respectively. The His(6)-tagged DAAO was expressed in E. coli and had a M-r value of approximately 39.3 kDa. In lactose-induced E . coli BL21 (DE3) (pET-DAAO), the expressed DAAO could comprise up to 15% o f total soluble proteins and a productivity of 23.4 U ml(-1) was obtained.