Silver inhibition on recombinant flavin reductase from Citrobacter freundii A1

Abstract

In this study, the flavin reductase (Fre) of Citrobatter freundii A1 was expressed in E. coli DH5a host with 1 mM IPTG induction. This recombinant protein was fused to 6xHis-tag, thus promising easier IMAC purification of the expressed enzyme. Flavin reductase catalyzes the reduction of free flavin using NADH to produce free reduced flavin. The purity of recombinant flavin reductase was observed using 15 % SDS-PAGE and the molecular weight of the target protein was determined to be 27.04 kDa. In this study, flavin reductase activity was measured at 340 nm (e340 = 6.22 mM-1cm-1) due to the oxidation of NADH. The effect of silver ions from silver nitrate (AgNO3) on the activity of flavin reductase was determined. As the concentration of silver ions increased, the relative activity and velocity of flavin reductase reaction decreased over time. Silver ions may inhibit flavin reductase irreversibly via unspecific binding to different amino acids. In conclusion, silver ions could be a potent inhibitor of flavin reductase of C. freundii A1.