Fatty Acid Anions Research Articles

Concentration effects in myoglobin-catalyzed peroxidation of linoleate.

The concentration of the free fatty acid anion linoleate was found to be important for the pro-oxidative activity of metmyoglobin, MbFe(III), and for mixtures of metmyoglobin and hydrogen peroxide, MbFe(III)/H(2)O(2), to yield perferrylmyoglobin, (*)MbFe(IV)=O, whereas for ferrylmyoglobin, MbFe(IV)=O, no concentration effect was noted as studied in linoleate emulsions (pH 7.4 and 25 degrees C). Determination of conjugated dienes using second-derivative absorption spectroscopy, changes in Soret band absorbance, and spin-trapping ESR spectroscopy with alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (POBN) as the spin trap were used to evaluate the pro-oxidative activity of myoglobins. At a linoleate (LA)/heme protein (HP) ratio of 100, no MbFe(III)-induced linoleate peroxidation was observed, as MbFe(III) was converted to its non-pro-oxidative low-spin derivative, hemichrome, independently of the presence of H(2)O(2). At higher LA/HP ratios, linoleate peroxidation was initiated by the addition of MbFe(III), both in the presence and in the absence of H(2)O(2). This proceeded with denaturation of MbFe(III), as followed by changes in Soret absorption band, which most probably release or expose the heme group to the environment and thereby permit hematin-induced lipid peroxidation. The obtained results show that the mechanism by which MbFe(IV)=O initiates linoleate peroxidation is different from MbFe(III)- and MbFe(III)/H(2)O(2)-initiated linoleate peroxidation. The shift in mechanism between heme protein cleavage of lipid hydroperoxides and hematin-induced lipid peroxidation is discussed in relation to oxidative progress in biological systems and muscle-based foods.

Mechanism of uncoupling protein action.

Two competing models of uncoupling protein (UCP) transport mechanism agree that fatty acids (FAs) are obligatory for uncoupling, but they disagree about which ion is transported. In Klingenberg's model, UCPs conduct protons. In Garlid's model, UCPs conduct anions, like all members of this gene family. In the latter model, UCP transports the anionic FA head group from one side of the membrane to the other, and the cycle is completed by rapid flip-flop of protonated FAs across the bilayer. The head groups of the FA analogues, long-chain alkylsulphonates, are translocated by UCP, but they cannot induce uncoupling, because these strong acids cannot be protonated for the flip-flop part of the cycle. We have overcome this limitation by ion-pair transport of undecanesulphonate with propranolol, which causes the sulphonate to deliver protons across the membrane as if it were an FA. Full GDP-sensitive uncoupling is seen in the presence of propranolol and undecanesulphonate. This result confirms that the mechanism of UCP uncoupling requires transport of the anionic FA head group by UCP and that the proton transport occurs via the bilayer and not via UCP.

An alternative function for human uncoupling protein 3: protection of mitochondria against accumulation of nonesterified fatty acids inside the mitochondrial matrix.

The physiological function of the human uncoupling protein 3 UCP3, which was discovered in 1997, is unknown. Here we evaluate the available data on human UCP3 expression and show that UCP3 is up-regulated in situations where fatty acid delivery to the mitochondria exceeds oxidative capacity, whereas down-regulation of UCP3 is observed when oxidative capacity is enhanced. With a surplus of fatty acid delivery, accumulation of nonesterified fatty acids in the cytoplasm is likely to occur. Although the inner mitochondrial membrane provides a barrier for nonesterified fatty acids, neutral nonesterified fatty acids can partition into the phospholipid bilayer and flip-flop to the other side of the membrane, where they can be released into the mitochondrial matrix. Due to pH differences, these nonesterified fatty acids will be protonated. Because fatty acid anions can neither be metabolized inside the matrix or cross the inner mitochondrial membrane, accumulation of nonesterified fatty acids inside the matrix might occur. Therefore, we postulate that UCP3 is required for the outward translocation of fatty acids from the mitochondrial matrix. In this way, UCP3 is involved in the protection of mitochondria against accumulation of nonesterified fatty acids inside the mitochondrial matrix.

Mechanism of uncoupling protein action

Two competing models of uncoupling protein (UCP) transport mechanism agree that fatty acids (FAs) are obligatory for uncoupling, but they disagree about which ion is transported. In Klingenberg's model, UCPs conduct protons. In Garlid's model, UCPs conduct anions, like all members of this gene family. In the latter model, UCP transports the anionic FA head group from one side of the membrane to the other, and the cycle is completed by rapid flip-flop of protonated FAs across the bilayer. The head groups of the FA analogues, long-chain alkylsulphonates, are translocated by UCP, but they cannot induce uncoupling, because these strong acids cannot be protonated for the flip-flop part of the cycle. We have overcome this limitation by ion-pair transport of undecanesulphonate with propranolol, which causes the sulphonate to deliver protons across the membrane as if it were an FA. Full GDP-sensitive uncoupling is seen in the presence of propranolol and undecanesulphonate. This result confirms that the mechanism of UCP uncoupling requires transport of the anionic FA head group by UCP and that the proton transport occurs via the bilayer and not via UCP.

Alkylsulfonates as Probes of Uncoupling Protein Transport Mechanism: ION PAIR TRANSPORT DEMONSTRATES THAT DIRECT H+TRANSLOCATION BY UCP1 IS NOT NECESSARY FOR UNCOUPLING

The mechanism of fatty acid-dependent uncoupling by mitochondrial uncoupling proteins (UCP) is still in debate. We have hypothesized that the anionic fatty acid head group is translocated by UCP, and the proton is transported electroneutrally in the bilayer by flip-flop of the protonated fatty acid. Alkylsulfonates are useful as probes of the UCP transport mechanism. They are analogues of fatty acids, and they are transported by UCP1, UCP2, and UCP3. We show that undecanesulfonate and laurate are mutually competitive inhibitors, supporting the hypothesis that fatty acid anion is transported by UCP1. Alkylsulfonates cannot be protonated because of their low pK(a), consequently, they cannot catalyze electroneutral proton transport in the bilayer and cannot support uncoupling by UCP. We report for the first time that propranolol forms permeant ion pairs with the alkylsulfonates, thereby removing this restriction. Because a proton is transported with the neutral ion pair, the sulfonate is able to deliver protons across the bilayer, behaving as if it were a fatty acid. When ion pair transport is combined with UCP1, we now observe electrophoretic proton transport and uncoupling of brown adipose tissue mitochondria. These experiments confirm that the proton transport of UCP-mediated uncoupling takes place in the lipid bilayer and not via UCP itself. Thus, UCP1, like other members of its gene family, translocates anions and does not translocate protons.

Precipitation and Solubility of Calcium Soaps in Basic Aqueous Media

Measurements of the surface tension of aqueous media containing calcium salts of different fatty acids, whose structure only varied by the number of C=C unsaturations along their aliphatic chains, showed that their solubility increased as a function of this parameter going from near zero for calcium stearate to 4×10−4 mol l−1 for the linolenate homologue. The solubility product of the calcium soap corresponding to each tested fatty acid was estimated by using the anionic fatty acids adsorption isotherms in order to obtain the amount of dissolved ionic fatty acid at increasing concentration of calcium ions. These findings are discussed in terms of their serious repercussions on the operations related to flotation deinking in waste paper recycling.

Characterization of polar lipids of oral isolates of Candida, Pichia and Saccharomyces by Fast Atom Bombardment Mass Spectrometry (FAB MS).

To characterize fatty acid and phospholipid analogue profiles of oral yeasts. Twenty-seven strains of oral yeasts were cultured on SDA and lipids of freeze-dried cells were extracted and analysed by FAB MS. The most abundant carboxylate anion was m/z 281 (C18 : 1). The most intense phospholipid analogue ions were of PE, PG, PA and PI. Pichia etchellsii contained molecular species of PG and PE, whereas Saccharomyces cerevisiae had PA, PG and PE analogues. Mass spectra revealed that S. cerevisiae and Candida glabrata were distinct from one another and from the other species tested. Oral yeasts largely differ with respect to their polar lipids. It is concluded that oral yeast species have distinctive fatty acid and phospholipid analogue anion profiles. FAB MS provided novel chemotaxonomic information.

Physiological role of UCP3 may be export of fatty acids from mitochondria when fatty acid oxidation predominates: an hypothesis.

This hypothesis proposes a physiological role for uncoupling protein-3 (UCP3) in the export of fatty acid anions from muscle and brown adipose tissue (BAT) mitochondria when fatty acids are the predominant substrate being used. It proposes that excess acyl CoA within the mitochondria is hydrolyzed by a mitochondrial acyl CoA thioesterase, yielding fatty acid anion and CoASH. The fatty acid anion is exported to the cytosol by being carried across the inner mitochondrial membrane by UCP3. The CoASH is conserved within the mitochondrion to participate in other reactions for which it is needed during fatty acid oxidation in the beta-oxidation cycle and in the tricarboxylic acid cycle. The export of the fatty acid anion thus permits continued rapid fatty acid oxidation in the face of an oversupply. The hypothesis provides a logical explanation for the observed up-regulation of gene expression for UCP3 in muscle when there is a switch to fatty acid oxidation, as during fasting, and in BAT when fatty acid oxidation is stimulated, as during exposure to cold. It provides a plausible physiological role for UCP3 as a transporter protein, not as an uncoupling protein.

Natural and Azido Fatty Acids Inhibit Phosphate Transport and Activate Fatty Acid Anion Uniport Mediated by the Mitochondrial Phosphate Carrier

The electroneutral P(i) uptake via the phosphate carrier (PIC) in rat liver and heart mitochondria is inhibited by fatty acids (FAs), by 12-(4-azido-2-nitrophenylamino)dodecanoic acid (AzDA) and heptylbenzoic acid ( approximately 1 microm doses) and by lauric, palmitic, or 12-azidododecanoic acids ( approximately 0.1 mm doses). In turn, reconstituted E. coli-expressed yeast PIC mediated anionic FA uniport with a similar pattern leading to FA cycling and H(+) uniport. The kinetics of P(i)/P(i) exchange on recombinant PIC in the presence of AzDA better corresponded to a competitive inhibition mechanism. Methanephosphonate was identified as a new PIC substrate. Decanephosphonate, butanephosphonate, 4-nitrophenylphosphate, and other P(i) analogs were not translocated and did not inhibit P(i) transport. However, methylenediphosphonate and iminodi(methylenephosphonate) inhibited both electroneutral P(i) uptake and FA cycling via PIC. AzDA analog 16-(4-azido-2-nitrophenylamino)-[(3)H(4)]-hexadecanoic acid ((3)H-AzHA) bound upon photoactivation to several mitochondrial proteins, including the 30- and 34-kDa bands. The latter was ascribed to PIC due to its specific elution pattern on Blue Sepharose and Affi-Gel. (3)H-AzHA photolabeling of recombinant PIC was prevented by methanephosphonate and diphosphonates and after premodification with 4-azido-2-nitrophenylphosphate. Hence, the demonstrated PIC interaction with monovalent long-chain FA anions, but with divalent phosphonates of short chain only, indicates a pattern distinct from that valid for the mitochondrial uncoupling protein-1.

Effect of the cationic detergent CTAB on the involvement of ADP/ATP antiporter and aspartate/glutamate antiporter in fatty acid-induced uncoupling of liver mitochondria.

The influence of the positively charged amphiphilic compound cetyltrimethyl ammonium bromide (CTAB) on palmitate- and laurate-induced uncoupling and on carboxyatractylate and glutamate recoupling effects in liver mitochondria have been studied. CTAB (40 microM) in the presence of 3 mM MgCl2 had little (if any) effect on the palmitic acid-stimulated respiration of mitochondria; the glutamate recoupling effect increased, and the carboxyatractylate recoupling effect decreased to the same degree with the combined effect (about 80%) remaining unchanged. Thus, CTAB decreases the ADP/ATP antiporter involvement and increases to the same extent the aspartate/glutamate antiporter involvement in the fatty acid-induced uncoupling. The carboxyatractylate and glutamate recoupling effects were less pH dependent in the presence of CTAB than in its absence. These data could be interpreted with the assumption that fatty acid anions are more accessible to the ADP/ATP antiporter and their neutral forms are more accessible to the aspartate/glutamate antiporter, and that CTAB changes the relative anion carrier involvement in the fatty acid-induced uncoupling as it forms neutral complexes with fatty acid anions.

How do uncoupling proteins uncouple?

According to the proton buffering model, introduced by Klingenberg, UCP1 conducts protons through a hydrophilic pathway lined with fatty acid head groups that buffer the protons as they move across the membrane. According to the fatty acid protonophore model, introduced by Garlid, UCPs do not conduct protons at all. Rather, like all members of this gene family, they are anion carriers. A variety of anions are transported, but the physiological substrates are fatty acid (FA) anions. Because the carboxylate head group is translocated by UCP, and because the protonated FA rapidly diffuses across the membrane, this mechanism permits FA to behave as regulated cycling protonophores. Favoring the latter mechanism is the fact that the head group of long-chain alkylsulfonates, strong acid analogues of FA, is also translocated by UCP.

Transport of heptafluorostearate across model membranes. Membrane transport of long-chain fatty acid anions I

Heptafluorostearic acid, an isogeometric derivative of stearic acid, has a pKa value of about 0.5. To evaluate the suitability of heptafluorostearate as model compound for anions of long-chain fatty acids in membrane transport, monolayer and liposome studies were performed with lipid mixtures containing phospholipids–cholesterol–heptafluorostearate or stearate (100:40:20 molar ratios). Transfer of heptafluorostearate and stearate from liposomes to bovine serum albumin (BSA) was followed by measuring the intrinsic fluorescence of BSA. The percentage of heptafluorostearate, equivalent to the amount placed in their outer monolayer, transferred from liposomes (120–130 nm diameter) to BSA was 55.7 ± 3.7% within 10 min at 25°C and 55 ± 2% within 5 min at 37°C. Slow transfer of 22.7 ± 2.5% of heptafluorostearate at 25°C followed with a half-life of 2.3 ± 0.4 h and of 20 ± 4% at 37°C with a half-life of 0.9 ± 0.1 h until the final equilibrium distributions between BSA and liposomes were reached, 79 ± 6% to 21 ± 5% at 25°C and 75 ± 5% to 25 ± 4% at 37°C. The pseudounimolecular rate constants for flip-flop of heptafluorostearate equal kFF,25 = 0.24 ± 0.05 h−1 and kFF,37 = 0.6 ± 0.1 h−1, respectively. By comparison, transfer of stearate required only 3 min to reach equilibrium distribution. The difference between heptafluorostearate and stearate may be explained by a rapid flip-flop movement of the un-ionized fatty acids which exist in different concentrations in accordance with their pKa values. Half-life of flip-flop of heptafluorostearate makes it suitable to study mediated membrane transport of long-chain fatty acid anions.—Schmider, W., A. Fahr, H. E. Blum, and G. Kurz. Transport of heptafluorostearate across model membranes. Membrane transport of long-chain fatty acid anions. I. J. Lipid Res. 2000. 41: 775–787.

Long-chain fatty acid-promoted swelling of mitochondria: further evidence for the protonophoric effect of fatty acids in the inner mitochondrial membrane

Swelling of non-respiring rat liver mitochondria suspended in isotonic potassium acetate at pH 6.5–7.4 in the presence of valinomycin was promoted by long-chain fatty acids, such as myristate, indicating a protonophoric mechanism. This swelling was partly inhibited by inhibitors or substrates of mitochondrial anion carriers. The results show that the fatty acid cycling mechanism responsible for uncoupling of oxidative phosphorylation can also operate in the direction opposite to that originally proposed [Skulachev, V.P. (1991) FEBS Lett. 294, 158–162], i.e. the inwardly directed transfer of the fatty acid anion accompanied by outwardly directed free passage of undissociated fatty acid. They also extend the list of mitochondrial anion carriers, that are involved in this process, over the mono- and tricarboxylate transporters. At pH 8, myristate, but not the synthetic protonophore, p-trifluoromethoxycarbonyl-cyanide phenylhydrazone, induced mitochondrial swelling in both potassium acetate and KCl media, that did not require the presence of valinomycin. This indicates that, at alkaline pH, myristate facilitates permeation of the inner mitochondrial membrane to monovalent cations and, possibly, activates the inner membrane anion channel.

Interaction of mitochondrial phosphate carrier with fatty acids and hydrophobic phosphate analogs

Mitochondrial transporters, in particular uncoupling proteins and the ADP/ATP carrier, are known to mediate uniport of anionic fatty acids (FAs), allowing FA cycling which is completed by the passive movement of FAs across the membrane in their protonated form. This study investigated the ability of the mitochondrial phosphate carrier to catalyze such a mechanism and, furthermore, how this putative activity is related to the previously observed HgCl 2-induced uniport mode. The yeast mitochondrial phosphate carrier was expressed in Escherichia coli and then reconstituted into lipid vesicles. The FA-induced H + uniport or Cl − uniport were monitored fluorometrically after HgCl 2 addition. These transport activities were further characterized by testing various inhibitors of the two different transport modes. The phosphate carrier was found to mediate FA cycling, which led to H + efflux in proteoliposomes. This activity was insensitive to ATP, mersalyl or N-ethylmaleimide and was inhibited by methylenediphosphonate and iminodi(methylenephosphonate), which are new inhibitors of mitochondrial phosphate transport. Also, the HgCl 2 induced Cl − uniport mediated by the reconstituted yeast PIC, was found to be inhibited by these reagents. Both methylenediphosphonate and iminodi(methylenephosphonate) blocked unidirectional Cl − uptake, whereas Cl − efflux was inhibited by iminodi(methylenephosphonate) and phosphonoformic acid only. These results suggest that a hydrophobic domain, interacting with FAs, exists in the mitochondrial phosphate carrier, which is distinct from the phosphate transport pathway. This domain allows for FA anion uniport via the phosphate carrier and consequently, FA cycling that should lead to uncoupling in mitochondria. This might be considered as a side function of this carrier.

Site-directed mutagenesis identifies residues in uncoupling protein (UCP1) involved in three different functions.

Using site-specific mutagenesis, we have constructed several mutants of uncoupling protein (UCP1) from brown adipose tissue to investigate the function of acidic side chains at positions 27, 167, 209, and 210 in H(+) and Cl(-) transport as well as in nucleotide binding. The H(+) transport activity was measured with mitochondria and with reconstituted vesicles. These mutant UCPs (D27N, D27E, E167Q, D209N, D210N, and D209N + D210N) are expressed at near wt levels in yeast. Their H(+) transport activity in mitochondria correlates well with the reconstituted protein except for D27N (intrahelical), which shows strong inhibition of H(+) transport in the reconstituted system and only 50% decrease of uncoupled respiration in mitochondria. In the double adjacent acidic residues (between helix 4 and helix 5), mutation of D210 and of D209 decreases H(+) transport 80% and only 20%, respectively. These mutants retain full Cl(-) transport activity. The results indicate that D210 participates in H(+) uptake at the cytosolic side and D27 in H(+) translocation through the membrane. Differently, E167Q has lost Cl(-) transport activity but retains the ability to transport H(+). The separate inactivation of H(+) and Cl(-) transport argues against the fatty acid anion transport mechanism of H(+) transport by UCP. The mutation of the double adjacent acidic residues (D209, D210) decreases pH dependency for only nucleoside triphosphate (NTP) but not diphosphate (NDP) binding. The results identify D209 and D210 in accordance with the previous model as those residues which control the location of H214 in the binding pocket, and thus contribute to the pH control of NTP but not of NDP binding.

Specific sequence of motifs of mitochondrial uncoupling proteins.

We have searched for the exclusivity of common sequence motifs of the mitochondrial uncoupling proteins (UCP1, UCP2, UCP3, UCP4, BMCP1, and plant UCP [PUMP]) within the gene family of mitochondrial anion carrier proteins. The UCP-specific sequences, "UCP signatures", were found in the first, second, and fourth alpha-helices. First: Ala/Ser-Cys/Thr/n-n/Phe-Ala/Gly-[negatively charged residue]-n/Phe-n/Cys-Thr-Phe/n; second: Gly/Ala-Ile/Leu-Gln/X-[positively charged residue]-NH-n/Cys-Ser/nphi/X-n/Ser-OH/Gly-n-[positively charged residue]-Ile/Met-Gly/Val-n/Thr; fourth: Pro-Asn/ Thr-n-X-[positively charged residue]-Asn/Ser/Ala-n-n-Ile/Leu-n-Asn/Val-Cys/n-n/Thr-[negatively charged residue]-n-n/Thr/Pro-OH/Val (n, nonpolar; phi, aromatic; (positively charged residue/negatively charged residue, charged residue). The second and part of the third signature are also present in the yeast dicarboxylate transporter. The UCP signature excluding BMCP1 was also found in the second matrix segment: [positively charged residue]-(Pro/ del-Leu/del)-[positively charged residue]-phi-X-Gly/Ser-Thr/n-X-NH/[negatively charged residue]-Ala-phi. These UCP signatures are thought to be involved in fatty acid anion binding and translocation.

Mixed-valence states of iron long-chain carboxylate complexes

Mixed-valence oxo-centered trinuclear iron carboxylate complexes with long alkyl-chain fatty acid anions, myristate [Fe 3O(O 2CC 13H 27) 6(py) 3], palmitate [Fe 3O(O 2CC 15H 31) 6(py) 3], stearate [Fe 3O(O 2CC 17H 35) 6(py) 3], and pyridine-solvated stearate [Fe 3O(O 2CC 17H 35) 6(py) 3]py, were studied by means of 57Fe Mössbauer spectroscopy. Each nonsolvated complex showed a temperature-dependent valence transformation between being valence-detrapped at room temperature (r.t.) and valence-trapped at low temperatures, while the solvated stearate complex showed a trapped-valence state at any temperature below r.t. The complexes showed no thermal anomaly in their DSC thermograms in the temperature range of 100–298 K, although the temperature dependence of the Mössbauer parameters and the powder X-ray diffraction patterns suggested a phase transition in the solvated stearate complex at ∼190 K.

Interaction of β-Cyclodextrin with Unsaturated and Saturated Straight Chain Fatty Acid Anions Studied by Phenolphthalein Displacement

The interaction of β-cyclodextrin (β-CD) with palmitoleate, linolenate, caprinate and caprylate was studied by the displacement of phenolphthalein (PHP) from the β-CD cavity. Absorbance values of β-CD–PHP solutions at 550 nm in 0.020 mol L-1 Na2CO3 buffer, pH 10.5, at 21.0 ± 0.5 °C, increased as the fatty acid anion was added. The concentration range of fatty acid anion used was 0.390–32.1 × 10-4 mol L-1 in the study of palmitoleate and linolenate, 1.92–80.0 × 10-4 mol L-1 in the study of caprinate and 0.770–32.0 × 10-3mol L-1 in the study of caprylate. Concentrations of β-CD and PHP were 1.00 × 10-3 mol L-1 and 1.00–3.00 × 10-4 mol L-1 respectively. Data were fitted by nonlinear regression to a two step complexation model. Complex formation constants thus determined for the 1 : 1 and 1 : 2, fatty acid anion : β-CD complex were: (1.2 ± 0.2) × 104 and (2.9 ± 0.2) × 102 mol-1 L for palmitoleate, (9.3 ± 0.9) × 103 and (1.1 ± 0.1) × 102 mol-1 L for linolenate, (4.1 ± 0.2) × 103 and 81 ± 8 mol-1 L for caprinate, and (5.2 ± 0.7) × 102 and 27 ± 5 mol-1 L for caprylate respectively. The PHP–β-CD complex was also evaluated as a spectrophotometric sensor for the determination of olive oil acidity.

The mechanisms of fatty acid-induced proton permeability of the inner mitochondrial membrane.

Nonesterified long-chain fatty acids have long been known as uncouplers of oxidative phosphorylation. They are efficient protonophores in the inner mitochondrial membrane but not so in artificial phospholipid membranes. In the un-ionized form, they undergo a rapid spontaneous transbilayer movement (flip-flop). However, the transbilayer passage of the dissociated (anionic) form is hindered by the negatively charged hydrophilic carboxylic group. In the inner mitochondrial membrane, the transfer of fatty acid anions is mediated by the adenine nucleotide translocase, the dicarboxylate carrier, and the glutamate/aspartate carrier. As a result, the passage of protons and electric charges is a concerted effect of the spontaneous flip-flop of the undissociated (protonated) form in one direction and carrier-facilitated transfer of the ionized (deprotonated) form in the other direction. In addition, fatty acids also promote opening of the mitochondrial permeability transition pore, presumably due to their interaction with one of its constituents, the adenine nucleotide translocase, thus forming an additional route for dissipation of the proton gradient. Structural prerequisites for these proton-conducting mechanisms are (1) a weakly ionized carboxylic group and (2) a hydrocarbon chain of appropriate length without substituents limiting its mobility and hydrophobicity.

Anion carriers in fatty acid-mediated physiological uncoupling.

Physiological aspects of uncoupling of oxidation and phosphorylation are reviewed in the context of involvement of mitochondrial anion carriers. It is assumed that the carriers facilitate electrophoretic translation of fatty acid anion, RCOO-, from the inner to the outer leaflet of the mitochondrial membrane, whereas back movement of the protonated fatty acid, RCOOH, from the outer to the inner leaflet represents flip-flop of RCOOH via the phospholipid bilayer of the membrane. The RCOO- transport seems to be catalyzed by the ATP/ADP and aspartate/ glutamate antiporters, dicarboxylate carrier, and uncoupling proteins (UCP1, UCP2, UCP3L, UCP3s, and plant UCP). The fatty acid uncoupling is shown to be involved in the thermoregulatory heat production in animals and plants exposed to cold, as well as in performance of respiratory functions other than ATP synthesis, i.e., formation of useful substances, decomposition of unwanted substances, and antioxidant defense. Moreover, partial uncoupling might take part in optimization of the rate of ATP synthesis in aerobic cells.