The nature and mechanism of action of uncoupling agents present in mitochrome preparations

Mitochondrial H+ Leak and Thermogenesis

Mitochondria of all tissues convert various metabolic substrates into two forms of energy: ATP and heat. Historically, the primary focus of research in mitochondrial bioenergetics was on the mechanisms of ATP production, while mitochondrial thermogenesis received significantly less attention. Nevertheless, mitochondrial heat production is crucial for the maintenance of body temperature, regulation of the pace of metabolism, and prevention of oxidative damage to mitochondria and the cell. In addition, mitochondrial thermogenesis has gained significance as a pharmacological target for treating metabolic disorders. Mitochondria produce heat as the result of H⁺ leak across their inner membrane. This review provides a critical assessment of the current field of mitochondrial H⁺ leak and thermogenesis, with a focus on the molecular mechanisms involved in the function and regulation of uncoupling protein 1 and the ADP/ATP carrier, the two proteins that mediate mitochondrial H⁺ leak.

Modulation and Pharmacology of the Mitochondrial Permeability Transition: A Journey from F-ATP Synthase to ANT

The permeability transition (PT) is an increased permeation of the inner mitochondrial membrane due to the opening of the PT pore (PTP), a Ca²⁺-activated high conductance channel involved in Ca²⁺ homeostasis and cell death. Alterations of the PTP have been associated with many pathological conditions and its targeting represents an incessant challenge in the field. Although the modulation of the PTP has been extensively explored, the lack of a clear picture of its molecular nature increases the degree of complexity for any target-based approach. Recent advances suggest the existence of at least two mitochondrial permeability pathways mediated by the F-ATP synthase and the ANT, although the exact molecular mechanism leading to channel formation remains elusive for both. A full comprehension of this to-pore conversion will help to assist in drug design and to develop pharmacological treatments for a fine-tuned PT regulation. Here, we will focus on regulatory mechanisms that impinge on the PTP and discuss the relevant literature of PTP targeting compounds with particular attention to F-ATP synthase and ANT.

Accumulation of nonesterified fatty acids causes the sustained energetic deficit in kidney proximal tubules after hypoxia-reoxygenation

Kidney proximal tubules exhibit decreased ATP and reduced, but not absent, mitochondrial membrane potential (Deltapsi(m)) during reoxygenation after severe hypoxia. This energetic deficit, which plays a pivotal role in overall cellular recovery, cannot be explained by loss of mitochondrial membrane integrity, decreased electron transport, or compromised F1F0-ATPase and adenine nucleotide translocase activities. Addition of oleate to permeabilized tubules produced concentration-dependent decreases of Deltapsi(m) measured by safranin O uptake (threshold for oleate = 0.25 microM, 1.6 nmol/mg protein; maximal effect = 4 microM, 26 nmol/mg) that were reversed by delipidated BSA (dBSA). Cell nonesterified fatty acid (NEFA) levels increased from <1 to 17.4 nmol/mg protein during 60- min hypoxia and remained elevated at 7.6 nmol/mg after 60 min reoxygenation, at which time ATP had recovered to only 10% of control values. Safranin O uptake in reoxygenated tubules, which was decreased 85% after 60-min hypoxia, was normalized by dBSA, which improved ATP synthesis as well. dBSA also almost completely normalized Deltapsi(m) when the duration of hypoxia was increased to 120 min. In intact tubules, the protective substrate combination of alpha-ketoglutarate + malate (alpha-KG/MAL) increased ATP three- to fourfold, limited NEFA accumulation during hypoxia by 50%, and lowered NEFA during reoxygenation. Notably, dBSA also improved ATP recovery when added to intact tubules during reoxygenation and was additive to the effect of alpha-KG/MAL. We conclude that NEFA overload is the primary cause of energetic failure of reoxygenated proximal tubules and lowering NEFA substantially contributes to the benefit from supplementation with alpha-KG/MAL.

Inhibitory effect of Mg2+ on the protonophoric activity of palmitic acid

To discriminate whether fatty acids are uncouplers that cause acceleration of State-4 respiration, associated with a decrease in the protonmotive force, or decouplers that increase respiration without associated decrease in the protonmotive force, we examined the effect of palmitate on functions of rat-liver mitochondria under various conditions. We found that palmitate itself increases State-4 respiration, releases oligomycin-inhibited State-3 respiration, inhibits ATP synthesis and ATP<->Pi exchange reaction, and increases H+ permeability in mitochondrial and model bilayer phospholipid membranes. Thus, palmitate is a classical uncoupler of oxidative phosphorylation. However, these effects were inhibited by Mg2+, due to rapid formation of a stable complex between palmitate and Mg2+.

Atherogenesis and fibrinogen: historical perspective and current status

A review of 117 research publications describes a deficiency in fatty acid transport into intracellular oxidative energy metabolism which causes increased fibrinogen synthesis and turnover into fibrin. The increased production of fibrin, coupled with depressed activation of plasminogen, increases the fibrin/plasmin ratio causing thrombosis-induced atherogenesis. This discovery unifies the two schools of atherogenesis based on blood lipid or fibrin deposition theories.

Effect of fatty acids on energy coupling processes in mitochondria

Long-chain fatty acids are natural uncouplers of oxidative phosphorylation in mitochondria. The protonophoric mechanism of this action is due to transbilayer movement of undissociated fatty acid in one direction and the passage of its anion in the opposite direction. The transfer of the dissociated form of fatty acid can be, at least in some kinds of mitochondrion, facilitated by adenine nucleotide translocase. Apart from dissipating the electrochemical proton gradient, long-chain fatty acids decrease the activity of the respiratory chain by mechanism(s) not fully understood. In intact cells and tissues fatty acids operate mostly as excellent respiratory substrates, providing electrons to the respiratory chain. This function masks their potential uncoupling effect which becomes apparent only under special physiological or pathological conditions characterized by unusual fatty acid accumulation. Short- and medium-chain fatty acids do not have protonophoric properties. Nevertheless, they contribute to energy dissipation because of slow intramitochondrial hydrolysis of their activation products, acyl-AMP and acyl-CoA. Long-chain fatty acids increase permeability of mitochondrial membranes to alkali metal cations. This is due to their ionophoric mechanism of action. Regulatory function of fatty acids with respect to specific cation channels has been postulated for the plasma membrane of muscle cells, but not demonstrated in mitochondria. Under cold stress, cold acclimation and arousal from hibernation the uncoupling effect of fatty acids may contribute to increased thermogenesis, especially in the muscle tissue. In brown adipose tissue, the special thermogenic organ of mammals, long-chain fatty acids promote operation of the unique natural uncoupling protein, thermogenin. As anionic amphiphiles, long-chain fatty acids increase the negative surface charge of biomembranes, thus interfering in their enzymic and transporting functions.

Serum and biliary lipid pattern in rabbits feeding a diet enriched with unsaturated fatty acids

Adult male New Zealand white rabbits were fed for 3 months a stock diet supplemented with 6% (w/w) soybean oil heated at 240 degrees C for 60 min. After the first month of treatment a significant increase in total lipid content of serum was observed mainly due to the cholesterol ester fraction. Simultaneously, grossly induced atherosclerosis and marked liver damage were histologically and clinically demonstrated. Lipid peroxide values, performed by thiobarbituric acid test in lipid extracts from liver, aorta and bile showed a significant increase as compared to controls. Lipoperoxidation rate increased with the duration of feeding. Parallel to this there was a marked reduction in the activities of glutathione peroxidase, superoxide dismutase and catalase in liver and aorta, all enzymes involved in the mechanism of detoxification of lipid peroxides. The results are in agreement with the hypothesis that lipid peroxidation can play a significant role in the pathogenesis of atherosclerosis.

Analysis of the regulation of phosphatidylinositol-4,5-bisphosphate synthesis by arachidonic acid in exocrine pancreas

In pancreatic acinar cells prelabeled with either 32Pi or myo-[3H]inositol, arachidonic acid (10-50 microM) rapidly decreased the steady-state levels of [32P]phosphatidylinositol 4',5'-bisphosphate [( 32P]PtdIns4,5P2) and inhibited carbachol-stimulated accumulation of [3H]inositol trisphosphate [( 3H]InsP3). Both actions of arachidonic acid were rapidly reversed by bovine serum albumin (BSA). Indomethacin and nordihydoguaiaretic acid failed to block the inhibitory effects of arachidonic acid on [32P]PtdIns4,5P2 levels. Arachidonic acid (10-50 microM) also caused a prompt depletion of cellular ATP which was rapidly reversed by BSA. The ATP-depleting action of arachidonate paralleled in terms of concentration dependence and time course its inhibitory effects on [32P]PtdIns4,5P2 and [3H]InsP3 levels. Exposure of acinar cells to 50 microM arachidonic acid produced an increase in oxygen consumption which exceeded that elicited by either carbachol or ionomycin. Arachidonic acid (10-50 microM) also caused a concentration-dependent rise in cytosolic Ca2+, which was partially obtunded by Ca2+ deprivation. A proposed mechanism involving arachidonic acid as a negative feedback regulator of polyphosphoinositide turnover in exocrine pancreas is discussed.

The ATP/ADP-antiporter is involved in the uncoupling effect of fatty acids on mitochondria

The ATP/ADP-antiporter inhibitors and the substrate ADP suppress the uncoupling effect induced by low (10-20 microM) concentrations of palmitate in mitochondria from skeletal muscle and liver. The inhibitors and ADP are found to (a) inhibit the palmitate-stimulated respiration in the controlled state and (b) increase the membrane potential lowered by palmitate. The degree of efficiency decreases in the order: carboxyatractylate (CAtr) greater than ADP greater than bongkrekic acid, atractylate. GDP is ineffective, Mg.ADP is of much smaller effect, whereas ATP is effective at much higher concentration than is ADP. Inhibitor concentrations, which maximally suppress the palmitate-stimulated respiration, correspond to those needed for arresting the state 3 respiration. The extent of the CAtr-sensitive stimulation of respiration by palmitate has been found to decrease with an increase in palmitate concentration. Stimulation of the controlled respiration by p-trifluoromethoxycarbonylcyanide phenylhydrozone (FCCP) and gramicidin D at any concentrations of these uncouplers is CAtr-insensitive, whereas that caused by a low concentrations of 2,4-dinitrophenol and dodecyl sulfate is inhibited by CAtr. The above effect of palmitate develops immediately after addition of the fatty acid. It is resistant to EGTA as well as to inhibitors of phospholipase (nupercain) and of lipid peroxidation (ionol). Moreover, palmitate accelerates spontaneous release of the respiratory control, developing in rat liver mitochondria under certain conditions. This effect takes several minutes, being sensitive to EGTA, nupercain and ionol. Like the fast uncoupling, this slow effect is inhibited by ADP but CAtr and atractylate are stimulatory rather than inhibitory. In artificial planar phospholipid membrane, palmitate does not increase the membrane conductance, FCCP increases it strongly and dinitrophenol only slightly. In cytochrome oxidase proteoliposomes, FCCP, gramicidin and dinitrophenol (less effectively) lower, whereas palmitate enhances the cytochrome-oxidase-generated membrane potential. In this system, monensin substitutes for palmitate. It is concluded that the ATP/ADP antiporter is somehow involved in the uncoupling effect caused by low concentrations of palmitate and, partially, of dinitrophenol, whereas uncoupling produced by FCCP and gramicidin is due to their action on the phospholipid part of the mitochondrial membrane. A possible mechanism of this effect is discussed.

Free fatty acids: a stimulus for mucin hypersecretion in cholesterol gallstone biles

The concentration of free fatty acids, phosphatidylcholine and lysophosphatidylcholine, and the fatty acid composition as well as the levels of the mucins, analyzed by an improved GLC method, were examined in ten biles from patients with cholesterol gallstones (pathological biles) and in ten control biles. In pathological biles the amounts of free fatty acids and phosphatidylcholine, were significantly higher (8.99 +/- 1.09) vs. 2.75 +/- 0.62 micrograms/mg) and lower (6.62 +/- 0.71 vs. 21.91 +/- 3.86 micrograms/mg), respectively, than in control biles, indicating that a relationship exists between the two lipid fractions. Lysophosphatidylcholine concentrations remained unchanged in the two groups (1.02 +/- 0.55 micrograms/mg in pathological biles vs. 1.32 +/- 0.57 micrograms/mg in control biles). The increased levels of free fatty acids were directly correlated (r = 0.73, P less than 0.05) with biliary hypersecretion of mucus glycoproteins. Acetylglucosamine and acetylgalactosamine were significantly higher in pathological biles than in control biles (1.91 +/- 0.67 vs. 0.60 +/- 0.13 microgram/mg). The nucleating potency of the increased amounts of mucins, coupled with lowered levels of phosphatidylcholine, might play a very important role in stone formation and precipitation.

The modes of action of long chain alkyl compounds on the respiratory chain-linked energy transducing system in submitochondrial particles

The interactions of long chain (greater than C7), alkyl compounds with tightly coupled, beef heart submitochondrial particles (SMP) have been investigated with respect to their effects upon respiratory chain-linked electron transfer and energy coupling capacity. Long chain alkyl alcohols, amines, free fatty acids, and methyl esters exhibit a general uncoupling effect, with stimulation of the succinate oxidase activity but inhibition of the NADH oxidase, in SMP. The degree of effectiveness is dependent on the nature of the functional group and the length of the alkyl chain. Submitochondrial particles depleted of F1 and the F1-inhibitor protein are similarly affected. Subsequent treatment with bovine serum albumin reverses the effects of free fatty acids and results in partial recovery of activity with alkyl amines, alcohols, and methyl esters. Differences between the effects of these alkyl compounds and those of sodium dodecyl sulfate, deoxycholate, palmitoyl carnitine, and palmitoyl CoA rule out detergent-like action as the explanation for these observations. These data suggest that specific lipophilic interactions with the membrane, modulated by the nature of the functional group, are responsible for the effects of these compounds on the energy transducing system of SMP. Analyses of the reduction kinetics of the cytochromes indicate that the sites of interaction of these compounds with the inner mitochondrial membrane are associated with the primary dehydrogenase of complex I and energy coupling site 2; alkyl amines possess an additional site of interaction in the region of complex III.

The role of mitochondrial calcium transport during inflammation and the effect of anti-inflammatory drugs

The effects of inflammation induced by the inoculation of rats with Freund's adjuvant on calcium transport by isolated rat liver mitochondria and on mitochondrial in vivo protein synthesis were investigated. Mitochondria isolated from the liver of inflamed rats exhibited (i) a reduction in 45Ca2+ uptake and, (ii) a reduction in protein synthesis. Addition of ATP to the calcium uptake medium stimulate the uptake in inflamed rat liver mitochondria. After inflammation was controlled by treatment with a mixture of Clerodendron inerme flavonoidal glycosides and indomethacin, rat liver mitochondria showed (i) an increase in 45Ca2+ uptake and, (ii) an increase in mitochondrial in vivo protein synthesis. The mechanism of mitochondrial calcium transport and the mitochondrial protein metabolism during inflammation and after treatment with anti-inflammatory drugs were discussed.

Limitation of myocardial infarct size by metabolic interventions that reduce accumulation of fatty acid metabolites in ischemic myocardium

The effects on myocardial damage of metabolic interventions by nicotinic acid, oxfenicine, or a combination of the two were assessed in open-chest dogs exposed to coronary artery occlusion for 6 hours. The accumulation of metabolites of free fatty acids (FFAs) was studied in tissue samples of the left ventricle taken 60 minutes after coronary occlusion in separate animals. The percentage of the hypoperfused zone that evolved to infarction was 96 +/- 3% (mean +/- SEM) in control dogs, 74 +/- 4% in dogs treated with nicotinic acid (p less than 0.05 vs control dogs), 72 +/- 2% in dogs treated with oxfenicine (p less than 0.05 vs control dogs), and 54 +/- 5% in dogs with combined nicotinic acid and oxfenicine (p less than 0.05 vs control dogs, p less than 0.05 vs nicotinic acid and oxfenicine). Arterial FFA concentration was markedly reduced in dogs treated with nicotinic acid and those treated with combination nicotinic acid and oxfenicine. The accumulation of long-chain acyl carnitine was substantially reduced in the ischemic myocardium after nicotinic acid, oxfenicine, and a combination of the two, whereas the lowering of long-chain acyl CoA was less pronounced. Thus, nicotinic acid and oxfenicine, which depress myocardial FFA metabolism by different mechanisms, both reduce myocardial infarct size and their effects are additive.

Effect of unsaturated fatty acids in growth inhibition of some penicillin-resistant and sensitive bacteria

The growth of two penicillin-resistant Gram-positive bacteria, Bacillus licheniformis (749/C, penicillin G-resistant) and Staphylococcus aureus (metR 18, methicillin-resistant) and one Gram-negative strain, Escherichia coli (cloxacillin-resistant) as well as that of their wild counterparts was inhibited by the long-chain unsaturated fatty acids, linoleic, linolenic and arachidonic acid. The minimum inhibitory concentrations (MIC) of all the fatty acids were found to be 4-6 micrograms/ml for Staph. aureus (metR 18 & wild), 8-30 micrograms/ml for B. licheniformis (749/C & wild) and 70-90 micrograms/ml for E. coli (cloxacillin-resistant & wild). The inhibitory activity increased as the number of double bonds in the fatty acids increased. In most instances the concentrations of fatty acids required to inhibit the growth of the penicillin-resistant strains were lower than that required for their sensitive counterparts. This inhibition of growth in the presence of fatty acids may be due to an increase in permeability of the membrane as evidenced by the measurement of the leakage of 260 nm absorbing material and fluidity.

Comparison of glucose, LCT, and LCT plus MCT as calorie sources for parenterally nourished rats

Protein and fat metabolism were studied in fed and protein-depleted rats. The rats were given one of three isocaloric, isonitrogenous nutrient mixes parenterally. The nutritional regimens differed in the source of nonprotein calories: i) glucose, ii) an emulsion containing long-chain fatty acid triglyceride esters (LCT), and iii) an emulsion containing both LCTs and medium-chain fatty acid triglycerides (MCT). Nitrogen balance, protein synthesis and breakdown, fat deposition in the liver, and the periuterine fat pads were measured using [15N]glycine as the tracer for the protein metabolism and deuterium for the lipid studies. Results are as follows. i) Nitrogen retention and protein synthesis were greater in the fed rats treated with glucose than with LCT. ii) Nitrogen fluxes were lower with LCT than with glucose. iii) Extensive lipogenesis in the liver was only found with the glucose-treated rats. iv) None of the caloric regimens promoted lipogenesis in the periuterine fat pads. v) With the two lipid-containing regimens there was a relative depletion of the depot fat in the periuterine fat pads relative to their glucose-treated counterparts. v) Although the MCT-containing emulsion did not cause hepatomegaly, its apparent caloric effectiveness was lower than that of either glucose or LCT. vi) Chain elongation is not a major pathway for MCT metabolism in parenterally nourished rats.

Cardiovascular actions of the calmodulin inhibitor felodipine

The cardiovascular effects of intravenous (1.5-10 nmol X kg-1) and intracoronary (50 nmol) administration of felodipine, 4-(2,3-dichlorophenyl)-1,4-dihydro-2, 6-dimethyl-3-ethoxycarbonyl-5-methoxycarbonylpyridine, were studied in anaesthetized pigs. Following intravenous administration dose-dependent decreases were observed in left ventricular systolic blood pressure (up to 30%) and in the resistances of the systemic (up to 40%) and coronary vascular beds (up to 45%), whereas heart rate, cardiac output, myocardial contractility (regional and global), and left ventricular end-diastolic pressure were minimally affected. Myocardial blood flow increased independently of the dose (20%), while the coronary venous O2-content more than doubled. The concomitant decrease in myocardial O2-consumption (up to 30%) was dose-dependent in the range from 1.5-6.75 nmol X kg-1. Intracoronary administration of 50 nmol had only minor effects on global and regional myocardial performance but produced a doubling of the coronary blood flow which was accompanied by a 70% decrease in myocardial O2-extraction. O2-consumption decreased considerably more (35%) than after intravenous administration in spite of the minimal decrease in O2-demand (7%). We conclude that felodipine dilates both systemic and coronary blood vessels. Although the reduction in myocardial O2-consumption is primarily caused by the reduction in afterload, a direct effect on myocardial metabolism can also be involved.

The composition of free fatty acids and mitochondrial activity in seedlings of winter cereals under cold shock

Cold shock (-4° C, 1 h) induces qualitative and quantitative changes in the composition of free fatty acids in mitochondria of winter-hardy cereals (Secale cereale L.,Triticum aestivum L.). The amount of these compounds and the degree of their unsaturation increases. Simultaneously, a marked change occurs in the oxidative and phophorylative activities of the mitochondria: respiratory control decreases, respiration in state 4 and antimycin A-resistant respiration increase. The changes in mitochondrial activity are presumed to be caused by endogenous free fatty acids, the amount of which is increased because of phospholipase activity.

Intracoronary infusion of small doses of nifedipine lowers regional myocardial O2-consumption without altering regional myocardial function

Intracoronary infusion of low doses (0.1-0.3 microgram X kg-1) of nifedipine caused dose-dependent decreases in regional myocardial O2-consumption, without significant changes in any of its major global hemodynamic determinants: heart rate, left ventricular systolic and end-diastolic pressure and maxLVdP/dt. Furthermore, regional myocardial function was unaltered. It is suggested that nifedipine decreased myocardial O2-consumption by a direct effect on myocardial metabolism. Some of the possible mechanisms involved are discussed.

Substrate effects on mitochondrial function and tissue lipids in low-flow hypoxia of isolated perfused rat hearts

A possible causal relationship between tissue FFA contents and the depression in mitochondrial oxidative phosphorylation in myocardial ischaemia has been suggested. To test this hypothesis, the effects of different substrates added to the perfusates of hypoxic, low-flow perfused hearts were examined on oxidative phosphorylation catalysed by mitochondria isolated from such tissue. In an additional series of experiments tissue neutral glyceride and FFA levels were analysed and correlated with changes in mitochondrial function. Mitochondria isolated from hearts with a high tissue FFA content exhibited the lowest ADP/O ratios, RCI and QO2 values. On the other hand, mitochondria isolated from hearts with reduced FFA contents, performed significantly better with respect to these parameters of mitochondrial function studied.

The oxidation of long-chain unsaturated fatty acids by isolated rat liver mitochondria as a function of substrate concentration

1. The oxidation of linoleate by rat-liver mitochondria has been studied as a function of substrate concentration. The oxidation of other long-chain unsaturated fatty acids shows similar characteristics. 2. At low concentrations, linoleate is readily oxidized in the absence of carnitine. Its rate of activation by the intramitochondrial acyl-CoA synthetase (EC 6.2.1.2) and subsequent oxidation is limited by the availability of intra-mitochondrial ATP. 3. A gradual increase of the linoleate concentration leads to (i) a strong depression of the rate of linoleate oxidation, and (ii) uncoupling of respiratory-chain phosphorylation together with induction of a mitochondrial ATPase activity. At still higher linoleate concentrations this ATPase activity is lowered rather than further stimulated and, concomitantly, the rate of linoleate oxidation increases again. 4. Evidence is presented that the inhibition by linoleate of the ATPase activity occurs at the level of the ATPase complex itself. This oligomycin-like effect of linoleate allows intramitochondrial linoleate activation to take place at the expense of ATP derived from substrate-level phosphorylation. 5. At very high concentrations of linoleate, its detergent action predominates and causes a complete inhibition of respiration as well as an extensive stimulation of an oligomycin-insensitive, Mg2+-dependent ATPase activity. 6. Measurement of the binding of radioactively labelled linoleate by isolated mitochondria shows that, at a given ratio of linoleate to mitochondrial protein, the ratio of bound to added linoleate is dependent on the concentration of the mitochondria.

Effect of insulin hypoglycemia upon cerebral energy metabolism and EEG activity in the rat

Anesthetized ventilated rats were subjected to insulin-induced hypoglycemia (50 units/kg i.v.) while EEG, ECG, mean arterial pressure, blood gases, arterial pH and rectal temperature were controlled. Animals were sacrificed by rapid transcalvarial freezing of the brain in situ. Glucose, pyruvate and lactate were measured in blood, CSF and cortical tissue, in which additionally glycogen, phosphocreatine, ATP, ADP, AMP, aketoglutarate (aKG), glutamate, oxalacetate, aspartate, ammonia and water content were estimated. ATP/ADP ratio, energy charge (ECh) energy reserve, NADH/NAD+ quotient and intracellular pH were calculated. ECh does not correlate with either dysfunction of carbohydrate depletion, but declines in a threshold fashion when tissue glucose has fallen by over 97% and glycogen by over 60%. The EEG correlates with the degree and duration of carbohydrate depletion in cortical tissue. An isoelectric EEG occurs pari passu with the fall of the ECh. Increase in ammonia and decrease in aKG and Glut are supportive evidence of intrinsic substrate. Lactate decrease during hypoglymecia is not reversed by super-imposed hyqoxia.

Effect of long-chain fatty acids and acyl-CoA on mitochondrial permeability, transport, and energy-coupling processes

The following effects of fatty acids and acyl-CoA thioesters on energy metabolism of mitochondria can now be assumed: (1) Inhibition of adenine nucleotide translocation. This effect may increase the energy state of mitochondria respiring under state 3 conditions and decrease phosphorylation potential in the surrounding medium (the cytoplasm). (2) Increased permeability to monovalent cations. This may lead to a partial energy dissipation due to a futile recycling of K+ (or another cation), namely and energy-dependent uptake and a passive outflow. (3) True uncoupling due to increased permeability to protons. This effect probably occurs at high concentrations of fatty acids only. (4) Substrate effect. Fatty acids in the form of acyl-CoA are excellent respiratory substrates for mitochondria of most tissues. Their oxidation is coupled to the generation of high energy state of the mitochondrial membrane and, consequently, to ATP synthesis.

Hamster brown-adipose-tissue mitochondria. The role of fatty acids in the control of the proton conductance of the inner membrane

The specific ability of fatty acids to increase the proton conductance of the inner membrane of mitochondria from the liver and brown adipose tissue of cold-adapted hamsters was compared. The liver and brown-adipose-tissue mitochondria had their effective proton conductances increased by respectively 0.028 and 0.94 nmol H+- min-1. (mV of proton electrochemical gradient)-1 for each nmol of palmitate bound. No difference could be detected between the abilities of liver and brown-adipose-tissue mitochondria to bind fatty acids. Purine nucleotides did not displace farry acids from the brown-adipase-tissue mitochondria. The endogenous fatty acid content of hamster brown-adipose-tissue mitochondria prepared in the absence of album was found to be equivalent to 17 +/- 7 nmol of palmitate/mg protein. The fatty acid content was reduced to 1 nmol/mg after preincubation of the mitochondria with CoA, ATP and carnitine. No inert pool of fatty acids could be detected. The endogenous fatty acids of hamster liver mitochondria were less than 4 nmol of palmitate equivalent/mg protein. Some of the fatty acid associated with the brown-adipose-tissue mitochondria originates during preparation of the mitochondria. In the light of these results, the physiological role of the fatty acids in controlling the proton conductance of the brown-adipose-tissue mitochondrial inner membrane, and hence- non-shivering thermogenesis, is re-evaluated.

Zonation of the adrenal cortex. II. Effect of BSA on coupling efficiency of mitochondria isolated from the zona glomerulosa of the bovine adrenal cortex

Effect of bovine serum albumin on coupling efficiency of mitochondria isolated from the zona glomerulosa of the bovine adrenal cortex in various media was examined polarographically and electron microscopically. Albumin restored the coupling efficiency of mitochondria isolated from the zona glomerulosa regardless of isolation media when succinate or malate was oxidizable substrate. Respiratory controls greater than 5 were obtained. Albumin, however, had no effect when glutamate, beta-hydroxybutylate and pyruvate were the oxidizable substrates. The conditions have been found under which mitochondria of the zona glomerulosa stay in the orthodox configuration and yet coupled.

Biogenesis of mitochondria. The effects of altered membrane lipid composition on cation transport by mitochondria of Saccharomyces cerevisiae

1. The fatty acid composition of the membrane lipids of a fatty acid desaturase mutant of Saccharomyces cerevisiae was manipulated by growing the organism in a medium containing defined fatty acid supplements. 2. Mitochondria were obtained whose fatty acids contain between 20% and 80% unsaturated fatty acids. 3. Mitochondria with high proportions of unsaturated fatty acids in their lipids have coupled oxidative phosphorylation with normal P/O ratios, accumulate K(+) ions in the presence of valinomycin and an energy source, and eject protons in an energy-dependent fashion. 4. If the unsaturated fatty acid content of the mitochondrial fatty acids is lowered to 20%, the mitochondria simultaneously lose active cation transport and the ability to couple phosphorylation to respiration. 5. The loss of energy-linked reactions is accompanied by an increased passive permeability of the mitochondria to protons. 6. Free fatty acids uncouple oxidative phosphorylation in yeast mitochondria and the effect is reversed by bovine serum albumin. 7. The free fatty acid contents of yeast mitochondria are unaffected by depletion of unsaturated fatty acids, and free fatty acids are not responsible for the uncoupling of oxidative phosphorylation in organelles depleted in unsaturated fatty acids. 8. It is suggested that the loss of energy-linked reactions in yeast mitochondria that are depleted in unsaturated fatty acids is a consequence of the increased passive permeability to protons, and is caused by a change in the physical properties of the lipid phase of the inner mitochondrial membrane.