The function of ubiquinone in Escherichia coli

Abstract

1. The function of ubiquinone in Escherichia coli was studied by using whole cells and membrane preparations of normal E. coli and of a mutant lacking ubiquinone. 2. The mutant lacking ubiquinone, strain AN59 (Ubi(-)), when grown under aerobic conditions, gave an anaerobic type of growth yield and produced large quantities of lactic acid, indicating that ubiquinone plays a vital role in electron transport. 3. NADH and lactate oxidase activities in membranes from strain AN59 (Ubi(-)) were greatly impaired and activity was restored by the addition of ubiquinone (Q-1). 4. Comparison of the percentage reduction of flavin, cytochrome b(1) and cytochrome a(2) in the aerobic steady state in membranes from the normal strain (AN62) and strain AN59 (Ubi(-)) and the effect of respiratory inhibitors on these percentages in membranes from strain AN62 suggest that ubiquinone functions at more than one site in the electron-transport chain. 5. Membranes from strain AN62, in the absence of substrate, showed an electron-spin-resonance signal attributed to ubisemiquinone. The amount of reduced ubiquinone (50%) found after rapid solvent extraction is consistent with the existence of ubiquinone in membranes as a stabilized ubisemiquinone. 6. The effects of piericidin A on membranes from strain AN62 suggest that this inhibitor acts at the ubiquinone sites: thus inhibition of electron transport is reversed by ubiquinone (Q-1); the aerobic steady-state oxidation-reduction levels of flavins and cytochrome b(1) in the presence of the inhibitor are raised to values approximating those found in the membranes of strain AN59 (Ubi(-)); the inhibitor rapidly eliminates the electron-spin-resonance signal attributed to ubisemiquinone and allows slow oxidation of endogenous ubiquinol in the absence of substrate and prevents reduction of ubiquinone in the presence of substrate. It is concluded that piericidin A separates ubiquinone from the remainder of the electron-transport chain. 7. A scheme is proposed in which ubisemiquinone, complexed to an electron carrier, functions in at least two positions in the electron-transport sequence.

Influence of Oxygen on Growth, Cytochrome Synthesis and Fermentation Pattern in Propionic Acid Bacteria

“…Because the oxidation-reduction potential of cytochrome a, is presumably rather high, its oxidation by fumarate might be an indirect effect. Experiments with HOQNO, known as an inhibitor of cytochrome b function (Cox et al 1970), indicate that cytochrome b functions directly in anaerobic electron transport from lactate to fumarate. To our knowledge little attention has been paid to the presence and function of cytochromes in anaerobic fermentative bacteria.…”

Dibromothymoquinone: An inhibitor of aerobic electron transport at the level of ubiquinone in Escherichia coli

“…DBMIB (50 PM)-inhibited NADH oxidase activity was not stimulated by the subsequent addition of an excess of ubiquinonei (280 PM), though DBMIBinhibited non-cyclic electron flow in chloroplasts has been shown previously to be competitively reversed by plastoquinone [lo]. Low concentrations of DBMIB 14 DBMIB also inhibits NADH-dependent cytochrome b reduction in E. coli membrane particles ( fig.3, compare traces A and B) indicating that DBMIB inhibition of electron transport occurs at the level of ubiquinone on the substrate side of the cytochromes as shown in scheme 1 [3,4]. However, the addition of DBMIB to KCN-inhibited particles results in the partial on cytochrome b reduction in particles from E. coli.…”

“…Perhaps the most promising application of ubiquinone analogues, like DBMIB, and also of menaquinone analogues, such as 2-hydroxy-3(cyclohexylpropyl)-14naph-thoquinone (an inhibitor of aerobic growth of Bacillus megaterium but not E. coli [ 12]), whose use as inhibitors of electron transport is restricted because of their auto-oxidation properties, is in the isolation of analogueresistant mutants. Whilst many of such mutants will no doubt have different permeability properties through alterations to the cell wall, the characterization of others should offer a complementary approach to previous investigations using mutants defective in their ability to synthesize either ubiquinone [3] or menaquinone [ 131 in the study of quinone function in electron transport.…”

“…Since there are few sitespecific inhibit0r.s of electron transport in Escherichia coli, other than KCN [3], we have investigated the effect of DBMIB on the growth and respiratory chain of aerobic cultures of this bacterium. In this paper we demonstrate that DBMIB inhibits: a) growth of the organism on a non-fermentatable carbon source, b) NADH, D-lactate and D,L a-glycerophosphate oxidase activities together with NADH-and D-lactate -DCPIP reductase activities of membrane particles, and c) NADH-dependent cytochrome b reduction.…”

A mutation affecting a second component of the F0 portion of the magnesium ion-stimulated adenosine triphosphatase of Escherichia coli K12. The uncC424 allele

“…Cells for the preparation of membranes were grown in 14-litre New Brunswick fermenters as described by Cox et al (1970).…”