Effects of Hydrogen Peroxide upon Nicotinamide Nucleotide Metabolism in Escherichia coli

Abstract

DNA is damaged in vivo (Fe 3؉ or Ga 3؉ ) with the adenine ring would bring it into close proximity to the redox-active nicotinamide ring in the folded form of NAD(P)H, but interaction of M 3؉ with the 2-phosphate group would avoid this close contact. In addition, as determined by absorbance spectroscopy, the energy of the charge-transfer species was significantly higher for the Fe 3؉ ⅐NADPH complex than for the Fe 3؉ ⅐NADH complex. We therefore suggest that upon exposure to H 2 O 2 the NADH pool is depleted, and NADPH, which is less reactive with Fe 3؉ , functions as the major nicotinamide nucleotide reductant.

The soxRS response of Escherichia coli can be induced in the absence of oxidative stress and oxygen by modulation of NADPH content

“…NADP + is synthesized from NAD + in a reaction catalysed by NAD + kinase. This enzyme does not belong to the soxRS regulon (Blanchard et al, 2007), and its activity did not increase when E. coli cells were exposed to micromolar concentrations of H 2 O 2 (Brumaghim et al, 2003). However, Grose et al (2006) showed that NAD + kinase is reversibly inhibited in vivo by NADPH.…”

“…1), so that they were not translated directly to NADPH : NADP + ratios. A major increase in the total (NADP + +NADPH) pool has been reported for the transition from anaerobic to aerobic lifestyles in E. coli (Brumaghim et al, 2003), and in the closely related species Salmonella enterica (Grose et al, 2006). NADP + is synthesized from NAD + in a reaction catalysed by NAD + kinase.…”

“…On exposure of E. coli cells to sublethal H 2 O 2 concentrations, two NADPH-producing enzymes were induced: G6PDH and respiration-dependent NADH-NADP + transhydrogenase, together with many scavenging and protective enzymes that oxidize NADPH (Brumaghim et al, 2003). In contrast, most NAD(H)-dependent dehydrogenases and reductases failed to respond to the oxidative challenge (Brumaghim et al, 2003). An even sharper labour division among NADHand NADPH-linked enzymes occurs in the soil microbe Pseudomonas fluorescens, which does not deploy a soxRStype response.…”

“…However, Grose et al (2006) showed that NAD + kinase is reversibly inhibited in vivo by NADPH. Since Brumaghim et al (2003) (Brumaghim et al, 2003) or as substrates for flavin reductase (Woodmansee & Imlay, 2002). Then, reduced pyridine nucleotides could have either protective or damaging effects during oxidative stress episodes, and therefore their cellular concentrations must be tightly regulated to ensure the welfare of the stressed organism.…”

“…Notably, several components of the soxRS and oxyR systems, such as glucose-6-phosphate dehydrogenase (G6PDH), ferredoxin-NADP(H) reductase (FPR), flavodoxin, GR and hydroperoxidase I are NADPHlinked enzymes or proteins. NADPH formation appears to be stimulated when bacteria are exposed to either superoxide radicals (Pomposiello et al, 2001) or H 2 O 2 (Brumaghim et al, 2003), suggesting that its accumulation is essential to cope with oxidative stress. On the other hand, high NADPH levels might have pro-oxidant effects by reducing transition metals to their more toxic states (Brumaghim et al, 2003).…”