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PubMed1982

Maintenance energy: a general model for energy-limited and energy-sufficient growth.

The new model proposed to account for the energy requirement for growth includes both a constant maintenance energy term (m) independent of the specific growth rate and a term (m') which decreases linearly with increase in specific growth rate and becomes zero at the maximum specific growth rate. The available data for testing the model do not deviate significantly from the relations predicted. Consistent values of the maximum growth yield (YG) can be derived, irrespective of whether the cultures are energy limited or energy sufficient. Attention is drawn to the possibility that the constant maintenance energy term may be estimated from the maximum specific growth rate.

Bacteria↗

PubMed1978

Relationship between iron-limited growth and energy limitation during phased cultivation of Candida utilis.

The yeast Candida utilis was continuously synchronized by the phasing technique (6 h doubling time) with either iron or nitrogen as the limiting nutrient. Iron limitations resulted in decreased molar growth yields with respect to the carbon substrates and ammonia and in increased specific rates of oxygen uptake. Relatively low energy-charge values were maintained by the iron-limited culture. All these taken together seemed to indicate that the growth of the yeast under iron limitation was also limited by metabolically available energy. Consideralbe amounts of ethyl acetate were produced by the yeast under phased cultivation when the growth was limited by iron but not by nitrogen. In vitro studies using cell-free extracts showed that the substrates for ethyl acetate synthesis were acetyl coenzyme A (acetyl CoA) and ethanol. Under iron-limited growth acetyl CoA seemed to be diverted to ethyl acetate formation rather than being oxidized through the tricarboxylic acid (TCA) cycle. The possibility of energy limitation under iron-limited growth being brought about by the reduced capacity of the yeast to oxidize acetyl CoA through the TCA cycle is considered.

Acetates↗

PubMed2002

Anisotropic free-energy limit of halos in high-intensity accelerators.

We study halo emittance growth in anisotropic beams and show that the rms emittance growth resulting from mismatch is highly anisotropic, depending on the tune ratio. We find that the free-energy limit calculated by Reiser [J. Appl. Phys. 70, 1919 (1991)] for an axisymmetric 1D halo can be extended to 2D if understood as an upper bound to the rms emittance growth averaged per degree of freedom. The thus-obtained "free-energy limit" of an ideal transport system is compared with the halo rms emittance growth in simulations of the Spallation Neutron Source linac.

Journal Article↗

PubMed2026

Effects of Short-Term Energy Limitation at Different Levels With Normal Protein Intake on Hepatic Lipid Metabolism and the Gut Microbiota in Overweight/Obese Mice.

This study investigated the sex-specific effects of graded short-term energy limitation (EL) with normal protein intake on hepatic lipid metabolism and the gut microbiota in overweight/obese mice. Mice were allocated to a normal control (NC) group, a high-fat diet model (MC) group, and groups receiving 20%, 30% or 40% EL (n = 8 per group). All mice underwent blood biochemistry, liver biochemistry, histological, liver metabolomic, and fecal microbiota community genomic analyses. Relative to the NC group, both male and female MC mice developed varying degrees of insulin resistance, dyslipidaemia, and sex hormone dysregulation. However, disrupted hepatic lipid metabolism was detected solely in male mice, in association with changes in key lipid-metabolizing enzymes and metabolites; female mice showed only disturbed total cholesterol (TC) metabolism, which was linked to alterations in the cholesterol synthesis rate-limiting enzyme HMGCR. With normal protein intake, 20%, 30%, and 40% EL reduced hepatic triglyceride and TC synthesis in overweight/obese male mice by suppressing the expression of the key lipogenic enzyme DGAT and the activities of ACC and HMGCR (p < 0.05). An effect on the lipolytic enzymes CPT1 and CYP7A1 was detected only at 30% EL (p < 0.05), and hepatic metabolite profiles varied with the degree of EL. In female mice, only 40% EL significantly decreased TC synthesis by inhibiting both HMGCR expression and enzymatic activity (p < 0.05). Furthermore, irrespective of sex, short-term EL (all levels) with normal protein intake reduced the gut Firmicutes/Bacteroidetes ratio in overweight/obese mice (p < 0.05). In conclusion, graded short-term EL with adequate protein intake exerts differential effects on hepatic lipid metabolism and the gut microbiota in overweight/obese mice, with pronounced sex-specific differences.

energy limitation↗

PubMed1977

Variations in the adenylate energy charge during phased growth (cell cycle) of Candida utilis under energy excess and energy-limiting growth conditions.

The variations in the levels of adenine nucleotides during the phased growth (cell cycle) of the yeast Candida utilis growing under nitrogen, sulfate, or iron limitation with glycerol as carbon source have been determined. Synchronous cultures were obtained by the continuous phasing technique, and the results were compared with those of chemostat cultures growing at similar growth rates and under the same types of nutrient limitation. Whereas the chemostat experiments indicated only the average energy status of cultures growing at random, results from phased cultures showed that the adenylate energy charge, defined as (ATP + (1/2)ADP)/(ATP + ADP + AMP) (where ATP, ADP, and AMP signify adenosine 5'-triphosphate, -diphosphate, and -monophosphate, respectively), varied during the phased growth of the yeast. These variations were related to the stage of development of the cells and to the type of nutrient limitation. In every case the energy charge dropped to a low value during the first half of the phasing cycle (cell cycle). Whereas the energy charge was maintained at relatively high levels (ranging from 0.78 to 0.94), for sulfate- or nitrogen-limited cultures, it was very low when iron was the growth-limiting nutrient (0.44 to 0.78). In spite of the low energy charge, the yeast continued to grow under iron limitation. The main component of the adenylate pool of the iron-limited culture was ADP and not ATP as observed with other types of nutrient limitation. It is concluded that under iron limitation the growth of the organism is limited by energy and that under energy-limited growth the energy charge of a growing organism is maintained at low levels. The reason for maintaining a low energy charge in an energy-limited culture is discussed.

Adenine Nucleotides↗

PubMed1997

Effects of energy limitation on Ca2+ and K+ homeostasis in anoxia-tolerant and anoxia-intolerant hepatocytes.

To gain more insight into the mechanistic basis of anoxia tolerance and intolerance, a comparative study was conducted on calcium homeostasis in goldfish and trout hepatocytes subjected to different forms of energy limitation. Using the fluorescent Ca2+ indicator fura 2, we observed that both chemical anoxia and true anoxia led to an increase of the concentration of cytosolic free calcium (Ca2+i) in the anoxia-sensitive hepatocytes of rainbow trout, whereas Ca2+i was maintained at control levels in the anoxia-tolerant hepatocytes of goldfish. Various lines of evidence suggest an intracellular origin of the Ca2+ increase observed in trout cells. Cyclosporin A, a specific inhibitor of the mitochondrial permeability transition pore in mammalian cells, was ineffective in preventing the Ca2+ increase, whereas a high dose of fructose depressed the Ca2+ surge by approximately 50%. The latter effect was not accompanied by improvement of the energetic state of the cells. A comparison of chemical anoxia with true (physiological) anoxia revealed that both treatments affected energy metabolism to a similar degree in trout hepatocytes, whereas the decrease of ATP seen in goldfish hepatocytes during chemical anoxia was absent during true anoxia. Elevation of Ca2+i with the calcium ionophore A-23187 led to a decoupling of unidirectional K+ fluxes in both normoxic and anoxic trout cells, whereas in goldfish hepatocytes the coupling of K+ fluxes was not affected by the rise of Ca2+i.

Adenosine Triphosphate↗

PubMed1976

Nitrate Reductase Activity in Soybeans (Glycine max [L.] Merr.): II. Energy Limitations.

Growth chamber studies with soybeans (Glycine max [L.] Merr.) were designed to determine the relative limitations of NO(3) (-), NADH, and nitrate reductase (NR) per se on nitrate metabolism as affected by light and temperature. Three NR enzyme assays (+NO(3) (-)in vivo, -NO(3) (-)in vivo, and in vitro) were compared. NR activity decreased with all assays when plants were exposed to dark. Addition of NO(3) (-) to the in vivo NR assay medium increased activity (over that of the -NO(3) (-)in vivo assay) at all sampling periods of a normal day-night sequence (14 hr-30 C day; 10 hr-20 C night), indicating that NO(3) (-) was rate-limiting. The stimulation of in vivo NR activity by NO(3) (-) was not seen in plants exposed to extended dark periods at elevated temperatures (16 hr-30 C), indicating that under those conditions, NO(3) (-) was not the limiting factor. Under the latter condition, in vitro NR activity was appreciable (19 mumol NO(2) (-) [g fresh weight, hr](-1)) suggesting that enzyme level per se was not the limiting factor and that reductant energy might be limiting.The addition of NADH to the in vivo NR assay medium did not stimulate NR activity, although it was not established that NADH entered the tissue. The addition of glucose, fructose 1,6-diphosphate, pyruvate, citrate, succinate, or malate to the in vivo assay medium significantly increased measurable NR activity of leaf tissue from plants pretreated to extended dark periods at elevated temperature. Glucose additions were most effective, usually stimulating increases 2- to 3-fold greater than the other metabolites. Increased NR activities from the various additives were attributed to production of NADH. The loss of in vivo NR activity in soybeans during darkness appeared to be due to the combination of a net loss of enzyme per se and energy depletion. The subsequent light stimulation of NR activity was likely due to increased availability of reductant energy as well as a net synthesis of the NR enzyme.

Journal Article↗

PubMed2004

Limits on the time variation of the electromagnetic fine-structure constant in the low energy limit from absorption lines in the spectra of distant quasars.

We present the results of a detailed many-multiplet analysis performed on a new sample of Mg ii systems observed in high quality quasar spectra obtained using the Very Large Telescope. The weighted mean value of the variation in alpha derived from our analysis over the redshift range 0.4</=z</=2.3 is Deltaalpha/alpha=(-0.06+/-0.06)x10(-5). The median redshift of our sample (z approximately 1.55) corresponds to a look-back time of 9.7 Gyr in the most favored cosmological model today. This gives a 3sigma limit, -2.5 x 10(-16)</=(Deltaalpha/alphaDeltat)</=+1.2 x 10(-16) yr(-1), for the time variation of alpha, that forms the strongest constraint obtained based on high redshift quasar absorption line systems.

Journal Article↗

PubMed1997

Ion homeostasis in brain cells: differences in intracellular ion responses to energy limitation between cultured neurons and glial cells.

Intracellular concentrations of sodium, potassium and calcium together with membrane potentials were measured in cultured murine cortical neurons and glial cells under conditions which mimicked in vivo hypoxia, ischemia and hypoglycemia. These included; glucose omission with and without added pyruvate, addition of rotenone in the presence and absence of glucose and substitution of 2-deoxyglucose for glucose with and without rotenone. Cellular energy levels ([ATP], [ADP], [phosphocreatine], [creatine]) were measured in suspensions of C6 cells incubated in parallel under identical conditions. [Na+]i and [Ca2+]i rose while [K+]i fell and plasma membrane depolarized when energy production was limited. Intracellular acidification was observed when glycolysis was the sole source for ATP synthesis. There was a positive correlation between the extent of energy depletion in glial cells and the magnitude and velocity of alterations in ion levels. Neither glycolysis alone nor oxidative phosphorylation alone were able to ensure unaltered ion gradients. Since oxidative phosphorylation is much more efficient in generating ATP than glycolysis, this finding suggests a specific requirement of the Na pump for ATP generated by glycolysis. Changes in [Na+]i and [K+]i observed during energy depletion were gradual and progressive whereas those in [Ca2+]i were initially slow and moderate with large elevations occurring only as a late event. Increases in [Na+]i were usually smaller than reductions in [K+]i, particularly in the glia, suggestive of cellular swelling. Glia were less sensitive to identical insults than were neurons under all conditions. Results presented in this study lead to the conclusion that the response to energy deprivation of the two main types of brain cells, neurons and astrocytes, is a complex function of their capacity to produce ATP and the activities of various pathways which are involved in ion homeostasis.

Adenosine Triphosphate↗

PubMed2005

Global physiological analysis of carbon- and energy-limited growing Escherichia coli confirms a high degree of catabolic flexibility and preparedness for mixed substrate utilization.

Growth conditions for heterotrophic bacteria in the environment are characterized by low concentrations of carbon and energy sources and complex substrate mixtures. While mechanisms of starvation-survival in the absence of carbon substrates have been studied in considerable detail, information on the physiology of slow growth under oligotrophic conditions is limited. We intended to elucidate general strategies by which Escherichia coli adapts to low concentrations of a mixed carbon and energy source pool. A new screening method based on BIOLOG AN MicroPlates, which allowed us to distinguish repressed and induced catabolic functions in E. coli, was combined with the analysis of periplasmic high-affinity binding proteins. Extending previous findings for E. coli and other microbial species, we found that numerous alternative catabolic functions and high-affinity binding proteins are derepressed under either glucose- or arabinose-limited growth conditions, in spite of the absence of the respective inducers. Escherichia coli cells growing in carbon-limited complex medium chemostat cultures exhibited an even higher degree of catabolic flexibility and were able to oxidize 43 substrates. The BIOLOG respiration pattern indicated simultaneous dissimilation of diverse sugars, amino acids and dipeptides (mixed substrate growth). The observed physiological adaptations of E. coli to low concentrations of carbon and energy substrates presumably are advantageous in many natural growth situations and also offer an explanation why many heterotrophic bacteria have and maintain such a broad carbon substrate range.

Bacteriological Techniques↗

PubMed1992

Rate-limiting energy-dependent steps controlling oxidative metabolism-contraction coupling in rabbit aorta.

1. We tested the hypotheses that coupling between oxidative metabolism and force in noradrenaline (NOR)-activated rabbit aorta is controlled (a) by an energy-dependent step or steps in receptor-operated coupling mechanisms upstream to myosin light chain (MLC) kinase, or (b) by energy limitation of MLC kinase-mediated phosphorylation of the MLC or actin-activated myosin ATPase. 2. Oxidative energy production was rapidly inhibited by decreasing organ bath PO2 to less than 30 mmHg. There was no difference, comparing KCl- or NOR-induced force, in the rates of decrease of [PCr] (phosphocreatine) or [ATP] following inhibition of oxidative energy production. (In this report we use the term [PCr] and [ATP] to indicate mean tissue values). Initial rates of decrease in [PCr] and [ATP] following inhibition of oxidative energy production were 0.05 mM/min and 0.06 mM/min, respectively. 3. Despite similar decreases in mean tissue [PCr] and [ATP], relaxations of KCl-induced contractions following inhibition of oxidative energy production were markedly delayed and were blunted compared to relaxations seen during NOR-induced contractions. The threshold mean tissue [PCr] and [ATP] for relaxation during KCl stimulation were 0.25 and 0.60 to 0.80 mM, respectively. During NOR stimulation, threshold values of [PCr] and [ATP] were 0.50 mM and 0.80 mM, respectively. Mean tissue [PCr] and [ATP] levels at 50% relaxation of KCl-induced force were less than 0.1 mM and 0.1 mM, respectively. Fifty per cent relaxation of NOR-induced force occurred at [PCr] and [ATP] values of 0.35 mM and 0.65 mM, respectively. 4. MLC phosphorylation levels decreased during relaxation of NOR force evoked by inhibition of oxidative energy production. There was no change in the level of MLC phosphorylation following inhibition of oxidative energy production in KCl-contracted muscle even at mean tissue [PCr] and [ATP] lower than values associated with decreases in MLC phosphorylation during relaxations of NOR-induced force. 5. Oxygen-induced redevelopment of force during NOR exposure was not dependent on extracellular Ca2+. Mean tissue [PCr] increased prior to onset of O2-evoked force redevelopment. Increases in MLC phosphorylation were seen at the time of onset of force redevelopment. 6. Oxidative metabolism-contraction coupling during NOR-stimulation seems not to be due to energy limitation of the MLC kinase reaction or actin-activated myosin ATPase. Data suggest the rate-limiting step is an energy-dependent reaction in receptor-operated coupling mechanisms upstream to MLC kinase.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗

PubMed1991

Physiological responses of soybean plants grown in a nitrogen-free or energy limited environment.

Soybean (Glycine max [L.] Merr.) seedlings grown in the absence of combined N and in an Ar:O(2) (79:21, volume/volume) atmosphere had greater seedling and nodule mass, threefold higher acetylene reducing activity per gram fresh weight nodules, no observable increase in nitrogenase Fe-protein, and a higher energy charge than did control plants. A sharp fall in acetylene reducing activity and energy charge accompanying stem-girdling was prevented by exogenous succinate, a result consistent with a path from the roots to the nodule other than via the phloem.

Journal Article↗

PubMed2006

Self-energy-limited ion transport in subnanometer channels.

The current-voltage characteristics of the alpha-Hemolysin protein pore during the passage of single-stranded DNA under varying ionic strength C are studied experimentally. We observe strong blockage of the current, weak superlinear growth of the current as a function of voltage, and a minimum of the current as a function of C. These observations are interpreted as the result of the ion electrostatic self-energy barrier originating from the large difference in the dielectric constants of water and the lipid bilayer. The dependence of DNA capture rate on C also agrees with our model.

Anions↗

PubMed2001

Pseudocapillarization and associated energy limitation in the aged rat liver.

Age-related impairment of drug metabolism by the liver is consistent with hepatocyte hypoxia, suggestive of the development of a diffusional barrier to oxygen supply. Because the effects of aging on the diffusional pathway (sinusoidal endothelium and space of Disse) have not been described, we performed comparative studies on the livers of Fischer F344 rats aged 4 to 7, 12 to 15, and 24 to 27 months. Light-microscopic examination revealed no evidence of fibrosis, cirrhosis, or other specific pathology. In contrast, scanning and transmission electron-microscopic examination revealed that aging is associated with pseudocapillarization of the sinusoidal endothelium, indicated by defenestration with reduced porosity, thickening of the endothelium, infrequent development of basal lamina, and only minor collagen deposits in the space of Disse. Furthermore, immunohistochemistry studies showed strong expression of collagen IV, moderate expression of factor VIII-related antigen, and weak expression of collagen I along the sinusoids of livers from old rats (P <.0001). In vitro (31)P magnetic resonance spectroscopy analysis showed that aging is associated with changes in high-energy phosphate and other metabolites, consistent with hepatocyte hypoxia. Aging in the liver is associated with changes in the sinusoidal endothelium and space of Disse that may restrict the availability of oxygen and other substrates.

Aging↗

PubMed1969