The relative contribution of membrane potential and pH gradient regulates mitochondrial oxygen consumption at constant proton motive force

Methanobacterium bryantii was grown on CO2 and H2 over a pH range between the extremes of 5.0 and 8.1. Generation times were shortest between pH 6.6 and 7.1. Cells grown at optimum pH had a proton motive force consisting predominantly of the membrane potential but those grown at nonoptimal pH generated a transmembrane pH gradient as well. This pH gradient was, however, insufficient to maintain a constant cytoplasmic pH during growth in very acidic or basic media. The results suggest that in acidic media growth may be limited by the cytoplasmic pH and that in alkaline media it may be limited by the cytoplasmic pH and (or) by the magnitude of the proton motive force.

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The effects of partial and selective reduction in the components of the proton-motive force on lactose uptake in Escherichia coli

Biochemical Journal ◽

10.1042/bj2000583 ◽

1981 ◽

Vol 200 (3) ◽

pp. 583-589 ◽

Cited By ~ 25

Author(s):

S Ahmed ◽

I R Booth

Keyword(s):

Escherichia Coli ◽

Steady State ◽

Membrane Potential ◽

Selective Reduction ◽

Proton Motive Force ◽

Motive Force ◽

Ph Gradient ◽

A Value ◽

The Relationship ◽

Lactose Transport

The relationship between the steady state lactose accumulation (delta plac) and the magnitude of the membrane potential (delta psi) and pH gradient (delta pH) has been studied at pHo5.5 and pHo7.5. An attempt has been made to differentiate between two possible means by which lactose accumulation may be reduced below the proton-motive force (delta p). Firstly, that delta psi and delta pH are not equivalent in driving lactose transport and secondly, that ‘slip’ reactions (beta-galactoside exit via the carrier without a proton) may reduce accumulation. The data support the latter; however, our conclusions are tempered by the observation that the apparent stoichiometry (delta plac/delta p) increases to a value of at least 2 at values of delta p below 130 mV.

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Dual Role for the Tyrosine Decarboxylation Pathway in Enterococcus faecium E17: Response to an Acid Challenge and Generation of a Proton Motive Force

Applied and Environmental Microbiology ◽

10.1128/aem.01958-08 ◽

2008 ◽

Vol 75 (2) ◽

pp. 345-352 ◽

Cited By ~ 38

Author(s):

C. I. Pereira ◽

D. Matos ◽

M. V. San Romão ◽

M. T. Barreto Crespo

Keyword(s):

Membrane Potential ◽

Enterococcus Faecium ◽

Proton Motive Force ◽

Motive Force ◽

Ph Gradient ◽

Ph Homeostasis ◽

Fermentation Products ◽

Cell Counts ◽

Acid Challenge

ABSTRACT In this work we investigated the role of the tyrosine decarboxylation pathway in the response of Enterococcus faecium E17 cells to an acid challenge. It was found that 91% of the cells were able to remain viable in the presence of tyrosine when they were incubated for 3 h in a complex medium at pH 2.5. This effect was shown to be related to the tyrosine decarboxylation pathway. Therefore, the role of tyrosine decarboxylation in pH homeostasis was studied. The membrane potential and pH gradient, the parameters that compose the proton motive force (PMF), were measured at different pHs (pH 4.5 to 7). We obtained evidence showing that the tyrosine decarboxylation pathway generates a PMF composed of a pH gradient formed due to proton consumption in the decarboxylation reaction and by a membrane potential which results from electrogenic transport of tyrosine in exchange for the corresponding biogenic amine tyramine. The properties of the tyrosine transporter were also studied in this work by using whole cells and right-side-out vesicles. The results showed that the transporter catalyzes homologous tyrosine/tyrosine antiport, as well as electrogenic heterologous tyrosine-tyramine exchange. The tyrosine transporter had properties of a typical precursor-product exchanger operating in a proton motive decarboxylation pathway. Therefore, the tyrosine decarboxylation pathway contributes to an acid response mechanism in E. faecium E17. This decarboxylation pathway gives the strain a competitive advantage in nutrient-depleted conditions, as well as in harsh acidic environments, and a better chance of survival, which contributes to higher cell counts in food fermentation products.

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Quantitative measurements of the proton-motive force and its relation to steady state lactose accumulation in Escherichia coli

Biochemical Journal ◽

10.1042/bj2000573 ◽

1981 ◽

Vol 200 (3) ◽

pp. 573-581 ◽

Cited By ~ 29

Author(s):

S Ahmed ◽

I R Booth

Keyword(s):

Escherichia Coli ◽

Steady State ◽

Membrane Potential ◽

Proton Motive Force ◽

Motive Force ◽

Ph Gradient ◽

Experimental Conditions ◽

Ph Values ◽

Quantitative Measurements ◽

Essential Prerequisite

The magnitude of delta psi (membrane potential), delta pH (pH gradient), lactose accumulation and cytoplasmic volume have been determined over a range of experimental conditions. A study of two probes of delta pH, benzoate and dimethyloxazolidene-2,4-dione (DMO), and four probes of delta psi, Rb+, K+, tetraphenylphosphonium (TPP+) and 3,3′-dipropylthiodicarbocyanine iodide, has been carried out. Benzoate and DMO are shown to be equivalent at pH values above the pK of DMO, but the latter may be less accurate below this pH. The cations TPP+ and Rb+ were found, by a number of criteria, to be equivalent, and TPP+ may be used in cells not pretreated with EDTA. These studies are an essential prerequisite to the use of TPP+ as a quantitative probe in untreated cells.

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Is Myelin a Mitochondrion?

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.2012.148 ◽

2012 ◽

Vol 33 (1) ◽

pp. 33-36 ◽

Cited By ~ 16

Author(s):

Julia J Harris ◽

David Attwell

Keyword(s):

Membrane Potential ◽

Respiratory Chain ◽

Atp Synthase ◽

Proton Motive Force ◽

Motive Force ◽

Myelin Membrane ◽

Considerable Doubt

It has been hypothesized that myelin acts like a mitochondrion, generating ATP across the membranes of its sheath. By calculating the proton motive force across the myelin membrane based on known values for the pH and membrane potential of the oligodendrocyte, we find that insufficient energy could be harvested from proton flow across the myelin membrane to synthesize ATP. In fact, if the respiratory chain were present in the myelin membrane, then the ATP synthase would function in reverse, hydrolyzing rather than synthesizing ATP. This calculation places the hypothesis of an energy-producing role for myelin in considerable doubt.

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