[37] Generation of a protonmotive force in anaerobic bacteria by end-product efflux

Tenbrink, B; Konings, Wn

doi:10.1016/s0076-6879(86)25039-9

Cited by 11 publications

(7 citation statements)

References 29 publications

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“…Pyruvate efflux in bloodstream forms appears to occur by facilitated diffusion through a monocarboxylate (pyruvate) transporter [8][9][10]. Previously identified monocarboxylate transporters in bacteria, yeast and mammalian cells transport substrates bidirectionally down their concentration gradient in symport with protons, and have an affinity for a limited repertoire of carboxylic acids [32][33][34][35][36]. To investigate the relationship between pyruvate efflux and regulation of pH i , inhibitors of pyruvate efflux, including pyruvate and various carboxylic acids that compete with pyruvate for the transporter, as well as the mitochondrial pyruvate transport inhibitor α-CHC, were examined for their effects on pH i and on proton and pyruvate efflux.…”

Section: Role Of the Pyruvate Transporter In Regulation Of Ph Imentioning

confidence: 99%

A pyruvate‒proton symport and an H+-ATPase regulate the intracellular pH of Trypanosoma brucei at different stages of its life cycle

Vanderheyden

Wong

Docampo³

2000

Biochem. J.

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Regulation of intracellular pH (pH(i)) and H(+) efflux were investigated in Trypanosoma brucei bloodstream and procyclic trypomastigotes using the fluorescent dyes 2', 7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) acetoxymethyl ester and free BCECF respectively. pH(i) in bloodstream and procyclic trypomastigotes was 7.47+/-0.06 and 7. 53+/-0.07 respectively. Differences in the mechanisms for the regulation of pH(i) were noted between bloodstream and procyclic forms. Procyclic trypomastigotes maintained their pH(i) at neutral over a wide range of external pH values from 6 to 8, and in the absence of K(+) or Na(+). The H(+)-ATPase inhibitors N, N'-dicyclohexylcarbodi-imide (DCCD), diethylstilboestrol and N-ethylmaleimide substantially decreased the steady-state pH(i) and inhibited its recovery from acidification. The rate of H(+) efflux in these forms was determined to be 62+/-6.5 nmol/min per mg of protein, and was substantially decreased by H(+)-ATPase inhibitors. The data support the presence of an H(+)-ATPase as the major regulator of pH(i) in procyclic trypomastigotes. In contrast, bloodstream trypomastigotes were unable to maintain a neutral pH under acidic conditions, and their steady-state pH(i) and recovery from acidification were unaffected by H(+)-ATPase inhibitors, except for DCCD (100 microM). Their steady-state pH(i) was markedly decreased in glucose-free buffer or by >/=10 mM pyruvate, whereas procyclic trypomastigotes were unaffected by similar treatments. The rate of H(+) efflux in bloodstream trypomastigotes was 534+/-38 nmol/min per mg of protein, and was decreased in the absence of glucose and by the addition of pyruvate or DCCD. Pyruvate efflux in these forms was calculated to be 499+/-34 nmol/min per mg of protein, and was significantly inhibited by DCCD, 4, 4'-di-isothiocyanatodihydrostilbene-2,2'-disulphonic acid and alpha-cyanohydroxycinnamic acid. The pyruvate analogues beta-hydroxypyruvate, 3-bromopyruvate, 3-oxoglutarate, oxaloacetate, 3-oxoisovalerate and 3-oxoisohexanoate significantly decreased pH(i), as well as proton and pyruvate efflux, whereas lactate had only a small effect, and no effect was observed with citrate or fumarate. The inhibition by pyruvate analogues of pyruvate efflux, proton efflux and acidification of pH(i) supports the hypothesis that pyruvate efflux is accompanied by proton efflux and that this is the major pH(i) control mechanism in bloodstream forms. Inhibition by H(+)-ATPase inhibitors of residual H(+) efflux in the absence of glucose or in the presence of high extracellular pyruvate indicates a minor role for H(+)-ATPase(s) in control of pH(i) in bloodstream forms.

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Section: Role Of the Pyruvate Transporter In Regulation Of Ph Imentioning

confidence: 99%

A pyruvate‒proton symport and an H+-ATPase regulate the intracellular pH of Trypanosoma brucei at different stages of its life cycle

Vanderheyden

Wong

Docampo³

2000

Biochem. J.

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“…Evidence has also been obtained that in some cases Δμ Η can be generated by metabolite fluxes (Michels et ai, 1979;Otto et ai, 1980;Ten Brink and Konings, 1980;Arshavsky et ai, 1981). Evidence has also been obtained that in some cases Δμ Η can be generated by metabolite fluxes (Michels et ai, 1979;Otto et ai, 1980;Ten Brink and Konings, 1980;Arshavsky et ai, 1981).…”

Section: δ/ι η As Output Force Of Redox and Atpase H + Pumpsmentioning

confidence: 99%

Determination of the Proton Electrochemical Gradient across Biological Membranes

Azzone

Pietrobon

Zoratti

1984

Current Topics in Bioenergetics

131

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“…This probably occurs because one additional ATP is formed per molecule of pyruvate through substrate-level phosphorylation concurrent with the formation of acetate (20). Michels' energy-recycling model has been proven for lactate and postulated for other organic acids, suggesting that acetate excretion may contribute to electrochemical proton gradient (25 TPP. After 1 min of incubation, 0.5 ml of silicone oil (density, 1.02 g/ml) was layered on top of the suspension.…”

mentioning

confidence: 99%

“…In this energy-recycling model, metabolic end products and protons are coexcreted via specific symport proteins in the cytoplasmic membrane. As result of this proton translocation, a PMF is generated which can contribute to the overall production of metabolic energy (23,25). Using Lactococcus cremoris, a homofermentative lactateproducing organism, as a model system, they observed that proton excretion coupled to lactate export supplied a significant quantity of metabolic energy to cells (17,18,24,26).…”

mentioning

confidence: 99%

Bioenergetic consequences of catabolic shifts by Lactobacillus plantarum in response to shifts in environmental oxygen and pH in chemostat cultures

1991

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Proton motive force (PMF), intracellular end product concentrations, and ATP levels were determined when a steady-state Lactobacillus plantarum 8014 anaerobic chemostat culture was shifted to an aerobic condition or was shifted from pH 5.5 to 7.5. The PMF and intracellular ATP levels increased immediately after the culture was shifted from anaerobic to aerobic conditions. The concentrations of intracellular lactate and acetate, which exported protons that contributed to the proton gradient, changed in the same fashion. The H+/lactate stoichiometry, n, varied from 0.8 to 1.2, and the H+/acetate n value changed from 0.8 to 1.6 at 2 h after the shift to aerobic conditions. The n value for acetate excretion remained elevated at aerobic steady state. When the anaerobic culture was shifted from pH 5.5 to 7.5, intracellular ATP increased 20% immediately even though the PMF decreased 50% as a result of the depletion of the transmembrane proton gradient. The H+/ lactate n value changed from 0.7 to 1.8, and n for H+/acetate increased from 0.9 to 1.9 at pH 7.5 steady state. In addition, the H+/acetate stoichiometry was always higher than the n value for H+/lactate; both were higher in alkaline than aerobic conditions, demonstrating that L. plantarum 8014 coexcreted more protons with end products to maintain intracellular pH homeostasis and generate proton gradients under aerobic and alkaline conditions. During the transient to pH 7.5, the n value for H+/acetate approached 3, which would spare one ATP.The circulation of ions across biological membranes, especially protons and sodium ions, is one of the fundamental processes in cellular energetics. Transport systems pump ions across membranes at the expense of some energy source, establishing an ion gradient whose electrochemical potential represents stored energy. Return of that ion across the membrane is mediated by a second transport system which links the downhill flux of the ion to the performance of some useful work (4).Mitchell's chemiosmotic hypothesis (13,14) proposed that electron transport and phosphorylation are not chemically linked, but are coupled by a transmembrane current of protons or proton motive force (PMF). The electron transport chain is a metabolic pathway arranged within and across the membrane to translocate protons across it. Since the membrane has a low conductance for protons and ions, a gradient of pH (ApH) and of membrane potential (A/@) will develop across the membrane to form the total PMF (AP) as given by the equation erichia coli. In this energy-recycling model, metabolic end products and protons are coexcreted via specific symport proteins in the cytoplasmic membrane. As result of this proton translocation, a PMF is generated which can contribute to the overall production of metabolic energy (23,25). Using Lactococcus cremoris, a homofermentative lactateproducing organism, as a model system, they observed that proton excretion coupled to lactate export supplied a significant quantity of metabolic energy to cells (17,18,24,26). Lactobacillu...

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[37] Generation of a protonmotive force in anaerobic bacteria by end-product efflux

Cited by 11 publications

References 29 publications

A pyruvate‒proton symport and an H+-ATPase regulate the intracellular pH of Trypanosoma brucei at different stages of its life cycle

A pyruvate‒proton symport and an H+-ATPase regulate the intracellular pH of Trypanosoma brucei at different stages of its life cycle

Determination of the Proton Electrochemical Gradient across Biological Membranes

Bioenergetic consequences of catabolic shifts by Lactobacillus plantarum in response to shifts in environmental oxygen and pH in chemostat cultures

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