Electrogenic Pumps

Spanswick, Roger M.

doi:10.1007/978-3-540-37843-3_10

Cited by 6 publications

(7 citation statements)

References 128 publications

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“…In addition to the sugar uptakes modeled in bna572 , developing embryonic tissues have other not fully characterized sugar transport mechanisms (Lichtner and Spanswick, 1981; Hay and Spanswick, 2007). Including a sucrose uniporter reaction in the plasma membrane to model a component of passive transport would make secondary active transport (#122) suboptimal, and raise the CCE because the coupled transport of sucrose and protons depends on the proton ATPase (Spanswick, 2006). However, the relative use of these parallel sucrose movements in vivo would depend on, among other things, the apoplastic sucrose concentration, which FBA does not account for.…”

Section: Discussionmentioning

confidence: 99%

Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to ¹³C metabolic flux analysis

Hay¹,

Schwender

2011

The Plant Journal

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SUMMARYPlant oils are an important renewable resource, and seed oil content is a key agronomical trait that is in part controlled by the metabolic processes within developing seeds. A large-scale model of cellular metabolism in developing embryos of Brassica napus (bna572) was used to predict biomass formation and to analyze metabolic steady states by flux variability analysis under different physiological conditions. Predicted flux patterns are highly correlated with results from prior 13 C metabolic flux analysis of B. napus developing embryos. Minor differences from the experimental results arose because bna572 always selected only one sugar and one nitrogen source from the available alternatives, and failed to predict the use of the oxidative pentose phosphate pathway. Flux variability, indicative of alternative optimal solutions, revealed alternative pathways that can provide pyruvate and NADPH to plastidic fatty acid synthesis. The nutritional values of different medium substrates were compared based on the overall carbon conversion efficiency (CCE) for the biosynthesis of biomass. Although bna572 has a functional nitrogen assimilation pathway via glutamate synthase, the simulations predict an unexpected role of glycine decarboxylase operating in the direction of NH 4 + assimilation. Analysis of the light-dependent improvement of carbon economy predicted two metabolic phases. At very low light levels small reductions in CO 2 efflux can be attributed to enzymes of the tricarboxylic acid cycle (oxoglutarate dehydrogenase, isocitrate dehydrogenase) and glycine decarboxylase. At higher light levels relevant to the 13 C flux studies, ribulose-1,5-bisphosphate carboxylase activity is predicted to account fully for the light-dependent changes in carbon balance.

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Section: Discussionmentioning

confidence: 99%

Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to ¹³C metabolic flux analysis

Hay¹,

Schwender

2011

The Plant Journal

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“…The electrical potential reflects the contributions of permeant ions and active transport; this is commonly summarized by the equation E m ϭ I pump /g m ϩ E G , which states that the membrane potential is the sum of pump current divided by conductance (I pump /g m ) and the Goldman-Hodgkin-Katz potential for permeant ions (E G ) (43). Conductance reflects the total value for voltage-dependent ion transport across the plasma membrane.…”

Section: Discussionmentioning

confidence: 99%

Mid1, a Mechanosensitive Calcium Ion Channel, Affects Growth, Development, and Ascospore Discharge in the Filamentous Fungus Gibberella zeae

et al. 2011

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The role of Mid1, a stretch-activated ion channel capable of being permeated by calcium, in ascospore development and forcible discharge from asci was examined in the pathogenic fungus Gibberella zeae (anamorph Fusarium graminearum). The ⌬mid1 mutants exhibited a >12-fold reduction in ascospore discharge activity and produced predominately abnormal two-celled ascospores with constricted and fragile septae. The vegetative growth rate of the mutants was ϳ50% of the wild-type rate, and production of macroconidia was >10-fold lower than in the wild type. To better understand the role of calcium flux, ⌬mid1 ⌬cch1 double mutants were also examined, as Cch1, an L-type calcium ion channel, is associated with Mid1 in Saccharomyces cerevisiae. The phenotype of the ⌬mid1 ⌬cch1 double mutants was similar to but more severe than the phenotype of the ⌬mid1 mutants for all categories. Potential and current-voltage measurements were taken in the vegetative hyphae of the ⌬mid1 and ⌬cch1 mutants and the wild type, and the measurements for all three strains were remarkably similar, indicating that neither protein contributes significantly to the overall electrical properties of the plasma membrane. Pathogenicity of the ⌬mid1 and ⌬mid1⌬cch1 mutants on the host (wheat) was not affected by the mutations. Exogenous calcium supplementation partially restored the ascospore discharge and vegetative growth defects for all mutants, but abnormal ascospores were still produced. These results extend the known roles of Mid1 to ascospore development and forcible discharge. However, Neurospora crassa ⌬mid1 mutants were also examined and did not exhibit defects in ascospore development or in ascospore discharge. In comparison to ion channels in other ascomycetes, Mid1 shows remarkable adaptability of roles, particularly with regard to niche-specific adaptation.

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“…The overall electrical potential (E m ) of the hypha depends on contributions from both the H ϩ -ATPase current and passive ion distributions across the membrane. This can be summarized by the equation E m ϭ I pump /g m ϩ E G , where I pump /g m is the H ϩ -ATPase current divided by the conductance and E G is the Goldman-Hodgkin-Katz potential for permeant ions (43). The conductance (g m ) is a measure of the overall electrogenic flux across the plasma membrane, which was unaffected in all of the mutants.…”

Section: Discussionmentioning

confidence: 99%

Electrical Phenotypes of Calcium Transport Mutant Strains of a Filamentous Fungus, Neurospora crassa

Hamam

Lew

2012

Eukaryot Cell

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We characterized the electrical phenotypes of mutants with mutations in genes encoding calcium transporters-a mechanosensitive channel homolog (MscS), a Ca 2؉ /H ؉ exchange protein (cax), and Ca 2؉ -ATPases (nca-1, nca-2, nca-3)-as well as those of double mutants (the nca-2 cax, nca-2 nca-3, and nca-3 cax mutants). The electrical characterization used dual impalements to obtain cable-corrected current-voltage measurements. Only two types of mutants (the MscS mutant; the nca-2 mutant and nca-2-containing double mutants) exhibited lower resting potentials. For the nca-2 mutant, on the basis of unchanged conductance and cyanide-induced depolarization of the potential, the cause is attenuated H ؉ -ATPase activity. The growth of the nca-2 mutant-containing strains was inhibited by elevated extracellular Ca 2؉ levels, indicative of lesions in Ca 2؉ homeostasis. However, the net Ca 2؉ effluxes of the nca-2 mutant, measured noninvasively with a self-referencing Ca 2؉ -selective microelectrode, were similar to those of the wild type. All of the mutants exhibited osmosensitivity similar to that of the wild type (the turgor of the nca-2 mutant was also similar to that of the wild type), suggesting that Ca 2؉ signaling does not play a role in osmoregulation. The hyphal tip morphology and tip-localized mitochondria of the nca-2 mutant were similar to those of the wild type, even when the external [Ca 2؉ ] was elevated. Thus, although Ca 2؉ homeostasis is perturbed in the nca-2 mutant (B. J. Bowman et al., Eukaryot. Cell 10:654 -661, 2011), the phenotype does not extend to tip growth or to osmoregulation but is revealed by lower H ؉ -ATPase activity.

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Electrogenic Pumps

Cited by 6 publications

References 128 publications

Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to ¹³C metabolic flux analysis

Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to ¹³C metabolic flux analysis

Mid1, a Mechanosensitive Calcium Ion Channel, Affects Growth, Development, and Ascospore Discharge in the Filamentous Fungus Gibberella zeae

Electrical Phenotypes of Calcium Transport Mutant Strains of a Filamentous Fungus, Neurospora crassa

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Electrogenic Pumps

Cited by 6 publications

References 128 publications

Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to 13C metabolic flux analysis

Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to 13C metabolic flux analysis

Mid1, a Mechanosensitive Calcium Ion Channel, Affects Growth, Development, and Ascospore Discharge in the Filamentous Fungus Gibberella zeae

Electrical Phenotypes of Calcium Transport Mutant Strains of a Filamentous Fungus, Neurospora crassa

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Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to ¹³C metabolic flux analysis

Computational analysis of storage synthesis in developing Brassica napus L. (oilseed rape) embryos: flux variability analysis in relation to ¹³C metabolic flux analysis