RESPONSE OF THE NAD(P)H-OXIDIZING FLAVOHAEMOGLOBIN (HMP) TO PROLONGEDOXIDATIVE STRESS AND IMPLICATIONS FOR ITS PHYSIOLOGICAL-ROLE IN ESCHERICHIA-COLI

The Escherichia coli flavohaemoglobin (Hmp) has a globin-like N-termin al domain and a ferredoxin-NADP-reductase-like C-terminal domain. We s how here that purified Hmp oxidises both NADH and NADPH with K-m value s of 1.8 and 19.6 mu M, respectively. Prolonged incubation of a hmp-la cZ fusion strain with the redox cycling agent paraquat resulted in a 2 8-fold induction of hmp gene expression, nearly 3-fold higher than aft er short periods of exposure. A strain overproducing Hmp was significa ntly more sensitive to paraquat than was the wild-type strain but, in vitro, purified Hmp was not an effective NADPH-paraquat diaphorase. Pr olonged incubation of a wild-type strain with paraquat increased intra cellular Hmp to spectrally detectable levels. (C) 1998 Federation of E uropean Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.