Routes of Flavodoxin and Ferredoxin Reduction in Escherichia coli

Abstract

Flavodoxin and ferredoxin become reduced in Escherichia coli cells by oxidoreductase reactions which use pyruvate and NADPH as electron donor substrates. The two enzymes, which are minor proteins of this organism, were measured through the reduced flavodoxin‐dependent activation of pyruvate formate‐lyase. The NADPH‐dependent enzyme, obtained homogeneously through Procion‐red affinity chromatography, was identified as the flavoprotein ‘component R’ described previously by Fujii and Huennekens [J. Biol. Chem. 249, 6745–6753 (1974)]. The pyruvate‐dependent enzyme was identified as CoA‐acetylating pyruvate; flavodoxin (ferredoxin) oxidoreductase. Its catalytic properties in the forward. reverse, and the 14CO2‐pyruvate exchange reaction are reported. The dihydro form of flavodoxin was characterized as the particular species involved in the activation of pyruvate formate‐lyase. The activation process still occurs with 70% of maximal efficiency when the ratio [NADPH]/([NADP] + [NADPH]) is fixed at the intracellular ‘anabolic reduction charge’ value of 0.45, in conjunction with the NADPH‐dependent enzyme. The [2Fe‐2S] ferredoxin, though being readily used as electron acceptor of both oxidoreductases and having a redox potential similar to flavodoxin, proved incompetent in mediating the activation of pyruvate formate‐lyase.

The Long and Short Flavodoxins

“…In nitrogen-fixing bacteria, such as Anabaena, flavodoxin is the electron donor for the nitrogenase iron-containing protein (31). In addition, flavodoxins can replace ferredoxin under certain conditions and have been shown to be substrates of the NAD-PH:ferredoxin oxidoreductase (FNR) of cyanobacteria (32) and of E. coli (33), of the pyruvate-ferredoxin oxidoreductase of Clostridium pasteurianum (34), and of the enzymes of dissimilatory sulfate reduction (35). Experimental evidence that the flavodoxin long loop could be involved in the interaction of E. coli flavodoxin with methionine synthase has already been provided by NMR mapping (36).…”

Crystal Structure and Functional Characterization of Yeast YLR011wp, an Enzyme with NAD(P)H-FMN and Ferric Iron Reductase Activities

“…This is accomplished by sandwiching the FMN ring between two hydrophobic side chains. Flavodoxins are involved in a variety of electron transfer reactions that are essential in the metabolism of pyruvate (2), nitrogen, and pyridine nucleotides (3). These enzymes exist under three redox states: oxidized; partially reduced (semiquinone); and fully reduced (hydroquinone).…”

High‐resolution crystal structures reveal a mixture of conformers of the Gly61‐Asp62 peptide bond in an oxidized flavodoxin from Bacillus cereus

“…Flavodoxins (Flds) are small electron transfer proteins that are involved in a variety of reactions in microorganisms. They participate, for example, in the photosynthetic reduction of NADP + , in nitrogen fixation, and in the reductive activation of various enzymes, such as pyruvate formate‐lyase, biotin synthase, ribonucleotide reductase, cytochrome P450 BioI, and bacterial nitric oxide synthase . Furthermore, Flds have been shown to be essential in some pathogenic bacteria, for example Helicobacter pylori and Streptococcus pneumoniae, and are therefore a potential drug target …”

“…They participate, for example, in the photosynthetic reduction of NADP 1 , in nitrogen fixation, and in the reductive activation of various enzymes, such as pyruvate formate-lyase, biotin synthase, ribonucleotide reductase, cytochrome P450 BioI, and bacterial nitric oxide synthase. [1][2][3][4][5][6][7][8] Furthermore, Flds have been shown to be essential in some pathogenic bacteria, for example Helicobacter pylori and Streptococcus pneumoniae, and are therefore a potential drug target. 9,10 Structurally, the Flds have a three-layer aba fold, consisting of a central five-stranded parallel b-sheet that is surrounded by two layers of a-helices.…”