NADPH-specific quinone reductase is induced by 2-methylene-4-butyrolactone in Escherichia coli

2-Methylene-4-butyrolactone (MBL), an inducer of NAD(P)H:(quinone acceptor) oxidoreductase (EC 1.699.2) in animal cells, was found to induce NADPH-specific quinone reductase about 25-fold in Escherichia coli. MBL induced NADPH-quinone reductases with relative mobilities (Rm) of 0.70, 0.76 and 0.91 on polyacrylamide gel electrophoresis (PAGE). These three enzymes were found to be charge isomers with the same molecular size of 42 kDA. Two NADPH-quinone reductases (A and B) were purified to single proteins both with an apparent mass of 21 kDa on SDS-PAGE. Enzyme A corresponded to the activity of the band at Rm 0.76 with a minor active band at Rm 0.70, and enzyme B to the activity of band Rm 0.91. Both enzymes reacted exclusively with NADPH and were most active toward quinone derivatives and ferricyanide with the optimum pH at 7.0. The reaction followed a ping-pong mechanism with Km values for NADPH and menadione of 10.5 microM and 6 microM, respectively. The sequences of 20 amino acids at the N-terminal of enzymes A and B were identical, and furthermore coincided with that of the E. coli modulator of drug activity (mda66) submitted under the accession number U18656.