Cloning and effective constitutive expression of aspC gene in escherichia coli

L-phenylalanine (L-Phe) can be prepared from phenylpyruvate (PPA) via an animation reaction mediated by aspartate aminotransferase (encoded by aspC) as the key enzyme. In this study, the aspC gene was cloned into plasmid pUC18, pSE 380 and pET-22b to construct three kinds of constitutive vectors, which were then transferred into 6 strains of Escherichia coli, respectively, to over-produce aminotransferase. From the transformants, the E. coli strain BL21(DE3) harboring plasmid pET/P-aspC showing the highest activity was scored and designated BL21(pET/P-aspC). With L-Asp and PPA (20 g/L) as substrates, the conversion rate reached 80.1% after eight-hour reaction, approaching the theoretical yield. This system had good industrial prospects because no inducer or coenzyme was needed. Furthermore, the results showed the potential of gene engineering on strain selections.