Efficiency Of Oxidative Phosphorylation Research Articles

Myocardial Impairment in Chronic Hypoxia is Abolished by Short Aeration Episodes: Involvement of K+ATP Channels

In vivo exposure to chronic hypoxia is considered to be a cause of myocardial dysfunction, thereby representing a deleterious condition, but repeated aeration episodes may exert some cardioprotection. We investigated the possible role of ATP-sensitive potassium channels in these mechanisms. First, rats (n = 8/group) were exposed for 14 days to either chronic hypoxia (CH; 10% O(2)) or chronic hypoxia with one episode/day of 1-hr normoxic aeration (CH+A), with normoxia (N) as the control. Second, isolated hearts were Langendorff perfused under hypoxia (10% O(2), 30 min) and reoxygenated (94% O(2), 30 min) with or without 3 microM glibenclamide (nonselective K(+)(ATP) channel-blocker) or 100 microM diazoxide (selective mitochondrial K(+)(ATP) channel-opener). Blood gasses, hemoglobin concentration, and plasma malondialdehyde were similar in CH and CH+A and in both different from normoxic (P < 0.01), body weight gain and plasma nitrate/nitrite were higher in CH+A than CH (P < 0.01), whereas apoptosis (number of TUNEL-positive nuclei) was less in CH+A than CH (P < 0.05). During in vitro hypoxia, the efficiency (ratio of ATP production/pressure x rate product) was the same in all groups and diazoxide had no measurable effects on myocardial performance, whereas glibenclamide increased end-diastolic pressure more in N and CH than in CH+A hearts (P < 0.05). During reoxgenation, efficiency was markedly less in CH with respect to N and CH+A (P < 0.0001), and ratex pressure product remained lower in CH than N and CH+A hearts (P < 0.001), but glibenclamide or diazoxide abolished this difference. Glibenclamide, but not diazoxide, decreased vascular resistance in N and CH (P < 0.005 and < 0.001) without changes in CH+A. We hypothesize that cardioprotection in chronically hypoxic hearts derive from cell depolarization by sarcolemmal K(+)(ATP) blockade or from preservation of oxidative phosphorylation efficiency (ATP turnover/myocardial performance) by mitochondrial K(+)(ATP) opening. Therefore K(+)(ATP) channels are involved in the deleterious effects of chronic hypoxia and in the cardioprotection elicited when chronic hypoxia is interrupted with short normoxic aeration episodes.

Oxidative stress in atherosclerosis‐prone mouse is due to low antioxidant capacity of mitochondria

Atherosclerotic disease remains a leading cause of death in westernized societies, and reactive oxygen species (ROS) play a pivotal role in atherogenesis. Mitochondria are the main intracellular sites of ROS generation and are also targets for oxidative damage. Here, we show that mitochondria from atherosclerosis-prone, hypercholesterolemic low-density lipoprotein (LDL) receptor knockout mice have oxidative phosphorylation efficiency similar to that from control mice but have a higher net production of ROS and susceptibility to develop membrane permeability transition. Increased ROS production was observed in mitochondria isolated from several tissues, including liver, heart, and brain, and in intact mononuclear cells from spleen. In contrast to control mitochondria, knockout mouse mitochondria did not sustain a reduced state of matrix NADPH, the main source of antioxidant defense against ROS. Experiments in vivo showed faster liver secretion rates and de novo synthesis of triglycerides and cholesterol in knockout than in control mice, suggesting that increased lipogenesis depleted the reducing equivalents from NADPH and generated a state of oxidative stress in hypercholesterolemic knockout mice. These data provide the first evidence of how oxidative stress is generated in LDL receptor defective cells and could explain the increased LDL oxidation, cell death, and atherogenesis seen in familiar hypercholesterolemia.

Modulation of hepatic mitochondrial energy efficiency with age.

This study was designed to examine the effect of youth-adulthood transition on hepatic mitochondrial energy efficiency. The changes in basal and palmitate-induced proton leak, which contribute to mitochondrial efficiency, were evaluated in mitochondria isolated from the liver of young and adult rats. Alterations in mitochondrial cytochrome oxidase and aconitase specific activities, and in adenine nucleotide translocator content were also assessed. There was no difference in basal proton leak or thermodynamic coupling and efficiency of oxidative phosphorylation in liver mitochondria between the two rat groups. On the other hand, palmitate-induced proton leak increased significantly in adult rats. The function of this uncoupling could be avoidance of elevated formation of reactive oxygen species, which are known to accelerate ageing.

The protective role of cellular glutathione peroxidase against trauma-induced mitochondrial dysfunction in the mouse brain

Reactive oxygen species are believed to participate in the pathogenesis of traumatic brain injury (TBI). To evaluate the role of cellular glutathione peroxidase (Gpx1), a selenium-containing enzyme functioning in reduction of hydrogen peroxide and alkyl hyperoxides, in protecting animals against TBI, a line of Gpx1 transgenic mice was generated. Overexpression of Gpx1 was found in many organs including the brain of the transgenic mice. This line of transgenic mice and knockout mice deficient in Gpx1 were used in a model of controlled cortical impact injury and the efficiency of oxidative phosphorylation in brain mitochondria was determined. Although a 2-mm depth of mechanical impact caused a drastic decrease in NAD-linked electron transfer activities and energy-coupling capacities in brain mitochondria of nontransgenic mice, the decrease in mitochondrial function was completely prevented by overexpression of Gpx1 in Gpx1 transgenic mice. In addition, a 1-mm deformation depth hardly affected brain mitochondrial function in wild-type (Gpx1 +/+) mice, yet resulted in a significant decrease in mitochondrial bioenergetic capacity in brains of homozygous Gpx1 knockout (Gpx1 −/−) mice. Further experiments showed that inclusion of calcium chelator egtazic acid in measurement of mitochondrial respiration could completely restore the efficiency of mitochondrial respiration in injured brains of nontransgenic mice and Gpx1 −/− mice, suggesting that the observed mitochondrial dysfunction is a direct result of increase in mitochondrion-associated calcium, which is secondary to the increased oxidative stress. These studies not only establish the role of Gpx1 in preventing mitochondrial dysfunction in mouse brain after TBI, but also suggest the species of reactive oxygen responsible for this event.

Protective Effect of EGb 761 Against Oxidative Phosphorylation of Brain Mitochondria After Anoxia/Reoxygenation In Vivo and In Vitro

The aim of this study was to investigate the effects of in vivo and in vitro anoxia and reoxygenation on the oxidative phosphorylation of brain mitochondria and to study the protective effects of Ginkgo biloba extract (EGb 761). Cerebral ischemia and reperfusion induced slight decreases in respiration rates and in the efficiency of oxidative phosphorylation. Total protection of mitochondrial function was observed after chronic pretreatment of rat with EGb 761. On the contrary, in vitro anoxia and reoxygenation of isolated brain mitochondria during respiratory assay promoted important alteration in respiration rates (around −50%) and in the oxidative phosphorylation yield (−44%). Partial protection was observed after anoxia and reoxygenation in the presence of EGb 761. Such a difference between in vivo and in vitro results could be explained by an intracellular antioxidant pool that could protect mitochondria in vivo.

Mitochondrial mechanism of heat stress-induced injury in rat cardiomyocyte

Heat stress results in cardiac dysfunction and even cardiac failure. To elucidate the cellular and molecular mechanism of cardiomyocyte injury induced by heat stress, the changes of structure and function in cardiac mitochondria of heat-exposed Wistar rats and its role in cardiomyocyte injury were investigated. Heat stress induced apoptosis and necrosis of cardiomyocytes in a time- and dose-dependent fashion. In the mitochondria of heat-stressed cardiomyocytes, the respiratory control rate and oxidative phosphorylation efficiency (P:O) were decreased gradually with the rise of rectal temperature. The Ca2+ -adenosine triphosphatase activity and Ca2+ content were also reduced. Exposing isolated mitochondria to the heat stress induced special internal environmental states including Ca2+ overload, oxidative stress, and altered mitochondrial membrane permeability transition (MPT). In vivo, the heat stress-induced mitochondrial MPT alteration was also found. The changes of mitochondrial MPT resulted in the release of cytochrome c from mitochondria into the cytosol, and in turn, caspase-3 was activated. Transfection of bcl-2 caused Bcl-2 overexpression in cardiomyocyte, which protected the mitochondria and reduced the heat stress-induced cardiomyocyte injury. In conclusion, it appears that the destruction of mitochondrial structure and function not only resulted in the impairment of physiological function of cardiomyocytes under heat stress but may also further lead to severe cellular injury and even cell death. These findings underline the contribution of mitochondria to the injury process in cardiomyocytes under heat stress.

Melatonin as an antioxidant: biochemical mechanisms and pathophysiological implications in humans.

This brief resume enumerates the multiple actions of melatonin as an antioxidant. This indoleamine is produced in the vertebrate pineal gland, the retina and possibly some other organs. Additionally, however, it is found in invertebrates, bacteria, unicellular organisms as well as in plants, all of which do not have a pineal gland. Melatonin's functions as an antioxidant include: a), direct free radical scavenging, b), stimulation of antioxidative enzymes, c), increasing the efficiency of mitochondrial oxidative phosphorylation and reducing electron leakage (thereby lowering free radical generation), and 3), augmenting the efficiency of other antioxidants. There may be other functions of melatonin, yet undiscovered, which enhance its ability to protect against molecular damage by oxygen and nitrogen-based toxic reactants. Numerous in vitro and in vivo studies have documented the ability of both physiological and pharmacological concentrations to melatonin to protect against free radical destruction. Furthermore, clinical tests utilizing melatonin have proven highly successful; because of the positive outcomes of these studies, melatonin's use in disease states and processes where free radical damage is involved should be increased.

Melatonin as an antioxidant: biochemical mechanisms and pathophysiological implications in humans.

This brief resume enumerates the multiple actions of melatonin as an antioxidant. This indoleamine is produced in the vertebrate pineal gland, the retina and possibly some other organs. Additionally, however, it is found in invertebrates, bacteria, unicellular organisms as well as in plants, all of which do not have a pineal gland. Melatonin's functions as an antioxidant include: a), direct free radical scavenging, b), stimulation of antioxidative enzymes, c), increasing the efficiency of mitochondrial oxidative phosphorylation and reducing electron leakage (thereby lowering free radical generation), and 3), augmenting the efficiency of other antioxidants. There may be other functions of melatonin, yet undiscovered, which enhance its ability to protect against molecular damage by oxygen and nitrogen-based toxic reactants. Numerous in vitro and in vivo studies have documented the ability of both physiological and pharmacological concentrations to melatonin to protect against free radical destruction. Furthermore, clinical tests utilizing melatonin have proven highly successful; because of the positive outcomes of these studies, melatonin's use in disease states and processes where free radical damage is involved should be increased.

Mitochondrial energy metabolism in a model of undernutrition induced by dexamethasone.

The present investigation was undertaken to evaluate whether mitochondrial energy metabolism is altered in a model of malnutrition induced by dexamethasone (DEX) treatment (1.5 mg/kg per d for 5 d). The gastrocnemius and liver mitochondria were isolated from DEX-treated, pair-fed (PF) and control (CON) rats. Body weight was reduced significantly more in the DEX-treated group (-16%) than in the PF group (-9%). DEX treatment increased liver mass (+59% v. PF, +23% v. CON) and decreased gastrocnemius mass. Moreover, in DEX-treated rats, liver mitochondria had an increased rate of non-phosphorylative O2 consumption with all substrates (approximately +42%). There was no difference in enzymatic complex activities in liver mitochondria between rat groups. Collectively, these results suggest an increased proton leak and/or redox slipping in the liver mitochondria of DEX-treated rats. In addition, DEX decreased the thermodynamic coupling and efficiency of oxidative phosphorylation. We therefore suggest that this increase in the proton leak and/or redox slip in the liver is responsible for the decrease in the thermodynamic efficiency of energy conversion. In contrast, none of the variables of energy metabolism determined in gastrocnemius mitochondria was altered by DEX treatment. Therefore, it appears that DEX specifically affects mitochondrial energy metabolism in the liver.

Comparison of the changes in adenine nucleotides of rat liver mitochondria induced by tamoxifen and 4-hydroxytamoxifen

The antiestrogen tamoxifen (TAM) inhibits the growth of different estrogen receptor (ER)-negative cells. Recently, multiple effects of TAM on mitochondrial bioenergetic functions have been pointed to explain its ER-independent cell death mechanisms. We have shown that TAM and its major active metabolite 4-hydroxytamoxifen (OHTAM) induce depolarization of the mitochondrial membrane potential (ΔΨ) and uncouple the mitochondrial respiration, depressing the oxidative phosphorylation efficiency. To clarify the biochemical mechanisms underlying the changes in the regulation of ATP synthesis and yield, in this work we evaluated the alterations of mitochondrial adenine nucleotides induced by both drugs and ascertained whether such changes could reflect a specific inhibition of either the adenine nucleotide translocase (ANT) or the phosphate carrier, as well as the activation of ATP hydrolysis due to ΔΨ depolarization. We found that both antiestrogens caused a concentration-dependent decrease in mitochondrial ATP levels. Mitochondrial ADP and AMP were concomitantly increased with a subsequent decrease in the ATP/ADP or ATP/AMP ratios. The total concentration of adenine nucleotides also changed. Additionally, both drugs decreased the ANT content of mitochondria, inhibited the phosphate carrier and induced ATP hydrolysis. However, the effects of TAM were more drastic than those induced by OHTAM. Therefore, the depletion of ATP might result from an activation of ATP catabolism, as well as from a decrease in the mitochondrial content of ANT and partial inhibition of the phosphate carrier. Our data may explain the ER-independent effects and cytotoxicity of both drugs and, in agreement with other previous studies, suggest that OHTAM is much less toxic to mitochondria than TAM.

The respiratory chain of Corynebacterium glutamicum

Corynebacterium glutamicum is an aerobic bacterium that requires oxygen as exogenous electron acceptor for respiration. Recent molecular and biochemical analyses together with information obtained from the genome sequence showed that C. glutamicum possesses a branched electron transport chain to oxygen with some remarkable features. Reducing equivalents obtained by the oxidation of various substrates are transferred to menaquinone via at least eight different dehydrogenases, i.e. NADH dehydrogenase, succinate dehydrogenase, malate:quinone oxidoreductase, pyruvate:quinone oxidoreductase, d-lactate dehydrogenase, l-lactate dehydrogenase, glycerol-3-phosphate dehydrogenase and l-proline dehydrogenase. All these enzymes contain a flavin cofactor and, except succinate dehydrogenase, are single subunit peripheral membrane proteins located inside the cell. From menaquinol, the electrons are passed either via the cytochrome bc 1 complex to the aa 3-type cytochrome c oxidase with low oxygen affinity, or to the cytochrome bd-type menaquinol oxidase with high oxygen affinity. The former branch is exceptional, in that it does not involve a separate cytochrome c for electron transfer from cytochrome c 1 to the Cu A center in subunit II of cytochrome aa 3. Rather, cytochrome c 1 contains two covalently bound heme groups, one of which presumably takes over the function of a separate cytochrome c. The bc 1 complex and cytochrome aa 3 oxidase form a supercomplex in C. glutamicum. The phenotype of defined mutants revealed that the bc 1– aa 3 branch, but not the bd branch, is of major importance for aerobic growth in minimal medium. Changes of the efficiency of oxidative phosphorylation caused by qualitative changes of the respiratory chain or by a defective F 1F 0-ATP synthase were found to have strong effects on metabolism and amino acid production. Therefore, the system of oxidative phosphorylation represents an attractive target for improving amino acid productivity of C. glutamicum by metabolic engineering.

Marked aging-related decline in efficiency of oxidative phosphorylation in human skin fibroblasts.

An extensive analysis has been carried out of mitochondrial biochemical and bioenergetic properties of fibroblasts, mostly skin-derived, from a large group of subjects ranging in age between 20 wk fetal and 103 yr. A striking age-related change observed in a fundamental process underlying mitochondrial biogenesis and function was the very significant decrease in rate of mitochondrial protein synthesis in individuals above 40 yr. The analysis of endogenous respiration rate revealed a significant decrease in the age range from 40 to 90 yr and a tendency to uncoupling in the samples from subjects above 60 yr. A surprising finding was the occurrence of a subgroup of individuals >or=90 yr old whose skin fibroblasts exhibited an exceptionally high respiration rate. This high rate was not due to respiration uncoupling, rather pointing to a compensatory phenomenon, not involving an increase in mtDNA content, in the corresponding skin fibroblast populations, or, possibly, to a selection of a different cell type secondary to more extensive dermal atrophy. The most important aging-related phenotypic effects observed were those that affected the cell oxidative phosphorylation (OX-PHOS) capacity. These were, in particular, the very significant reduction in the ratio of uncoupled to oligomycin-inhibited endogenous respiration observed in intact fibroblasts, which pointed to a decrease with donor's age in the control of respiration by the mitochondrial membrane potential, the very significant decrease in efficiency of OX-PHOS, as determined by novel in situ measurements of P:O ratios, and, consistent with these results, the very significant reduction in the respiratory control ratios. These findings clearly pointed to a dramatic mitochondrial dysfunction, which would lead to a decrease in ATP synthesis rate, with the observed decline in mitochondrial protein synthesis rate being a likely contributing factor. These observations have important implications for understanding the biology of aging, as well as the pathogenesis of aging-related degenerative diseases.

The efficiency of functional mitochondrial replacement in Saccharomyces species has directional character.

Optimal interactions among nuclear and mitochondria-coded proteins are required to assemble functional complexes of mitochondrial oxidative phosphorylation. The communication between the nuclear and mitochondrial genomes has been studied by transplacement of mitochondria from related species into mutants devoid of mitochondrial DNA (rho0). Recently we have reported that the mitochondria transferred from Saccharomyces paradoxus restored partially the respiration in Saccharomyces cerevisiae rho0 mutants. Here we present evidence that the S. cerevisiae mitochondria completely salvage from respiration deficiency, not only in conspecific isolates but also in S. paradoxus. The respiratory capacity in less-related species can be recovered exclusively in the presence of S. cerevisiae chromosomes. The efficiency of the re-established oxidative phosphorylation did not rely on the presence of introns in the S. cerevisiae mitochondrial DNA. Our results suggest that, apart from evolutionary distance, the direction of mitochondrial replacement could play a significant role in installing the complete (wild-type-like) interaction between mitochondria and nuclei from different species.

Delta sleep inducing peptide (DSIP): effect on respiration activity in rat brain mitochondria and stress protective potency under experimental hypoxia

Neuromodulatory delta sleep inducing peptide (DSIP) seems to be implicated in the attenuation of stress-induced pathological metabolic disturbances in various animal species and human beings. Mitochondria, as cell organelles, are considered especially sensitive to stress conditions. In this work, the influence of DSIP and Deltaran ®—a recently developed product based upon DSIP—on processes of oxidative phosphorylation and ATP production in rat brain mitochondria and rat brain homogenates was studied. A polarographic measurement of oxygen consumption was applied to evaluate the impact of DSIP on maximal rates of mitochondrial respiration and coupling of respiration to ATP production. We provide evidence that DSIP affected the efficiency of oxidative phosphorylation on isolated rat brain mitochondria. This peptide significantly increased the rate of phosphorylated respiration V3, while the rate of uncoupled respiration V DNP remaining unchanged. It enhanced the respiratory control ratio RCR and the rate of ADP phosphorylation. DSIP and Deltaran exhibited the same action in rat brain homogenates. We also examined the influence of DSIP under hypoxia when mitochondrial respiratory activity is altered. In rats subjected to hypoxia, we detected a significant stress-mediated reduction of V3 and ADP/t values. Pretreatment of rats with DSIP at the dose of 120 μg/kg (i.p.) prior to their subjection to hypoxia completely inhibited hypoxia-induced reduction of mitochondrial respiratory activity. The revealed capacity of DSIP to enhance the efficiency of oxidative phosphorylation found in vitro experiments could contribute to understanding pronounced stress protective and antioxidant action of this peptide in vivo.

Assessing metabolic activity in aging Caenorhabditis elegans: concepts and controversies.

It is widely believed that normal by-products of oxidative metabolism and the subsequent molecular damage inflicted by them couple the aging process to metabolic rate. Accordingly, high metabolic rates would be expected to accelerate aging, and life-extending interventions are often assumed to act by attenuating metabolic rate. Notorious examples in Caenorhabditis elegans are food restriction, mutation in the Clock genes and several genes of the insulin-like signalling pathway. Here we discuss how metabolic rate can be accurately measured and normalized, and how to deal with differences in body size. These issues are illustrated using experimental data of the long-lived mutant strains clk-1(e2519) and daf-2(e1370). Appropriate analysis shows that metabolic rates in wildtype and in the clk-1 mutant are very similar. In contrast, the metabolic rate profiles point to a metabolic shift toward enhanced efficiency of oxidative phosphorylation in the daf-2 worms.

Mitochondrial Respiratory Chain Adjustment to Cellular Energy Demand

Because adaptation to physiological changes in cellular energy demand is a crucial imperative for life, mitochondrial oxidative phosphorylation is tightly controlled by ATP consumption. Nevertheless, the mechanisms permitting such large variations in ATP synthesis capacity, as well as the consequence on the overall efficiency of oxidative phosphorylation, are not known. By investigating several physiological models in vivo in rats (hyper- and hypothyroidism, polyunsaturated fatty acid deficiency, and chronic ethanol intoxication) we found that the increase in hepatocyte respiration (from 9.8 to 22.7 nmol of O(2)/min/mg dry cells) was tightly correlated with total mitochondrial cytochrome content, expressed both per mg dry cells or per mg mitochondrial protein. Moreover, this increase in total cytochrome content was accompanied by an increase in the respective proportion of cytochrome oxidase; while total cytochrome content increased 2-fold (from 0.341 +/- 0.021 to 0.821 +/- 0.024 nmol/mg protein), cytochrome oxidase increased 10-fold (from 0.020 +/- 0.002 to 0.224 +/- 0.006 nmol/mg protein). This modification was associated with a decrease in the overall efficiency of the respiratory chain. Since cytochrome oxidase is well recognized for slippage between redox reactions and proton pumping, we suggest that this dramatic increase in cytochrome oxidase is responsible for the decrease in the overall efficiency of respiratory chain and, in turn, of ATP synthesis yield, linked to the adaptive increase in oxidative phosphorylation capacity.

Morphofunctional mitochondrial response to methylglyoxal toxicity in Bufo bufo embryos

Methylglyoxal (2-oxopropanal) is a reactive α-oxoaldehyde that can be formed endogenously mainly as a by-product of glycolytic pathway. It is a cytotoxic compound with significant antiproliferative properties as it can bind, under physiological conditions, to nucleic acids and proteins, forming stable adducts. We have recently shown that exogenous methylglyoxal (150–600 μM) is highly toxic for amphibian embryos where it produces, when added to the culture water, inhibition of cell proliferation in the early developmental stages, followed by severe malformations and strongly reduced embryonic viability. In this work we investigate the morphofunctional effect of methylglyoxal on the common toad B. bufo embryo mitochondria in order to verify if its dysmorphogenetic action might be also ascribed to impairment of mitochondrial functions. The mitochondria were isolated from embryos at the developmental stages of morula, neural plate and operculum complete and developing in the presence of 600 μM methylglyoxal. The results show that exogenous methylglyoxal is highly toxic at mitochondrial level, where it produces proliferation, swelling and membrane derangement. As a consequence, mitochondria from treated embryos show decreased oxidative phosphorylation efficiency, as indicated by the significant reduction both of the respiratory control index values and of the embryonic ATP content. On the basis of these data, it is possible that the methylglyoxal-induced embryonic malformations as well as the strongly reduced viability might be also ascribed to energy depletion.

Role of substrates in the regulation of mitochondrial function in situ.

Investigations of mitochondrial oxidative phosphorylation have been mainly carried out in isolated mitochondria, where the experimental conditions can be precisely set. However, in intact living systems oxidative phosphorylation takes place in a complex environment, whose experimental dissection is a major challenge. It has long been recognized that the efficiency of oxidative phosphorylation depends on the nature of the respiratory substrates, which feed electrons to the respiratory chain at different levels. Yet, the role of substrates in determining mitochondrial function and their response to energetic stress has been largely overlooked. Here we review recent work showing that the nature of the energetic substrates profoundly affects the mitochondrial responses to manipulations of pathophysiological relevance, such as uncoupling and opening of the permeability transition pore (PTP). Uncoupling of intact hepatocytes caused very different metabolic effects depending on whether carbohydrates or lipids were the energy source. With dihydroxyacetone as the substrate dinitrophenol caused a collapse of the mitochondrial membrane potential and of the ATP/ADP ratio, while the respiratory rate was increased only transiently. With octanoate as the substrate, on the other hand, dinitrophenol caused a dramatic stimulation of the respiratory rate, while the mitochondrial membrane potential and ATP/ADP ratio were affected only marginally. We then review results indicating that the activity of complex I directly regulates the PTP, a finding that emphasizes the importance of the respiratory substrates in PTP regulation.

Glycogen metabolism in aerobic mixed cultures.

In this study, the metabolism of glycogen storage and consumption in mixed cultures under aerobic conditions is described. The experimental results are used to calibrate a metabolic model, which as sole stoichiometric variables has the efficiency of oxidative phosphorylation (delta) and maintenance requirement in units of adenosine triphosphate (m(ATP)). Using the experimental data and values from the literature we show that delta and m(ATP) are strongly coupled and that the values determined for glycogen and poly-beta-hydroxybutyrate (PHB) metabolism are similar. We also demonstrate that storage of glycogen and subsequent growth occur without significant loss of energy, as compared with direct growth on glucose. For kinetic modeling, Monod kinetics is used most commonly in activated sludge models to describe the rate of microbial transformation. Monod kinetics, however, does not provide a good description of the data obtained. Second-order kinetics gives a better description of the rate of glycogen degradation. Formation and consumption of glycogen appears to be much faster than for PHB.

Mitochondrial adaptation to in vivo polyunsaturated fatty acid deficiency: increase in phosphorylation efficiency.

Polyunsaturated fatty acid (PUFA) deficiency affects respiratory rate both in isolated mitochondria and in hepatocytes, an effect that is normally ascribed to major changes in membrane composition causing, in turn, protonophoriclike effects. In this study, we have compared the properties of hepatocytes isolated from PUFA-deficient rats with those from control animals treated with concentrations of the protonophoric uncoupler 2,4-dinitrophenol (DNP). Despite identical respiratory rate and in situ mitochondrial membrane potential (delta psi), mitochondrial and cytosolic ATP/ADP-Pi ratios were significantly higher in PUFA-deficient cells than in control cells treated with DNP. We show that PUFA-deficient cells display an increase of phosphorylation efficiency, a higher mitochondrial ATP/ADP-Pi ratio being maintained despite the lower delta psi. This is achieved by (1) decreasing mitochondrial Pi accumulation, (2) increasing ATP synthase activity, and (3) by increasing the flux control coefficient of adenine nucleotide translocation. As a consequence, oxidative phosphorylation efficiency was only slightly affected in PUFA-deficient animals as compared to protonophoric uncoupling (DNP). Thus, the energy waste induced by PUFA deficiency on the processes that generate the proton motive force (pmf) is compensated in vivo by powerful adaptive mechanisms that act on the processes that use the pmf to synthesize ATP.