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Teruel T, Hernandez R, Rial E, Martin-Hidalgo A, Lorenzo M. Rosiglitazone up-regulates lipoprotein lipase, hormone-sensitive lipase and uncoupling protein-1, and down-regulates insulin-induced fatty acid synthase gene expression in brown adipocytes of Wistar rats. Diabetologia 2005; 48:1180-8. [PMID: 15887043 DOI: 10.1007/s00125-005-1744-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2004] [Accepted: 12/30/2004] [Indexed: 11/24/2022]
Abstract
AIMS/HYPOTHESIS Although thiazolidinediones are now widely used to treat type 2 diabetes, their mechanism of action remains largely unknown. They are agonists for the transcription factor PPARgamma, and in addition to their insulin-sensitising effects, they can promote adipogenesis and control gene expression in adipose tissues. We have explored the effect of rosiglitazone on insulin-mediated induction of pivotal genes involved in lipid metabolism and thermogenesis in brown fat. The genes studied were: (1) lipoprotein lipase (lpl), which is involved in lipid uptake; (2) hormone-sensitive lipase (hsl), which mobilises fatty acids from stored triglycerides; (3) fatty acid synthase (fas), which regulates de novo lipogenesis; and (4) the uncoupling proteins (ucp) 1 and 3, which control thermogenesis. METHODS We used fetal rat primary brown adipocytes cultured with insulin, rosiglitazone or both combined. Then, we studied gene expression by northern and western blotting, as well as 'run-on' and gel-shift assays to identify binding of potential transcription factors to the fas promoter. RESULTS Exposure to rosiglitazone for 24 h induced ucp-1, lpl and hsl gene expression and when rosiglitazone was combined with insulin a synergistic effect on lpl and ucp-3 mRNA expression was produced. These effects were consistent with increased LPL and HSL activities as well as respiration rates, mainly in response to exogenous palmitate. In contrast, treatment with rosiglitazone did not alter FAS mRNA basal levels but prevented the induction elicited by insulin in a time- and dose-dependent manner. Correspondingly diminished FAS protein levels and activity, as well as cellular lipid content, were observed, indicating an antilipogenic action of rosiglitazone in brown adipocytes. Furthermore, rosiglitazone impaired insulin increase in the FAS transcription rate by antagonising insulin-induced binding of upstream stimulatory factors to the E-box consensus sequence in the FAS promoter and insulin-induced binding of activating protein-1. CONCLUSIONS/INTERPRETATION Rosiglitazone prevents insulin-induced up-regulation of the main lipogenic enzyme but increases the expression of those enzymes involved in lipid uptake and mobilisation, favouring fatty acid utilisation through uncoupled respiration.
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Affiliation(s)
- T Teruel
- Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, Complutense University, 28040, Madrid, Spain
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Abelenda M, Ledesma A, Rial E, Puerta M. Leptin administration to cold-acclimated rats reduces both food intake and brown adipose tissue thermogenesis. J Therm Biol 2003. [DOI: 10.1016/s0306-4565(03)00053-6] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Rodriguero MS, Vera MT, Rial E, Cayol JP, Vilardi JC. Sexual selection on multivariate phenotype in wild and mass-reared Ceratitis capitata (Diptera: Tephritidae). Heredity (Edinb) 2002; 89:480-7. [PMID: 12466992 DOI: 10.1038/sj.hdy.6800170] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2002] [Accepted: 07/28/2002] [Indexed: 11/09/2022] Open
Abstract
Males with a larger thorax and narrower face were found to be favoured by directional sexual selection in a previous field cage experiment where Ceratitis capitata males from the Seib 6-96 genetic sexing strain competed with wild males from Alto Valle (Patagonia) for the possession of wild females. Targets of sexual selection, however, might differ between wild and laboratory females as a response to adaptation to mass-rearing conditions. To evaluate possible divergences on the targets of sexual selection as a by-product of adaptation to mass-rearing conditions, field cage tests were performed with both wild and laboratory females. To avoid possible bias due to correlation among the measured traits (eye length [EL], face width [FW], head width [HW], and thorax length [TL]), a multivariate analysis was applied. Consistent with the previous experiment, the results indicated that TL and FW are probable targets of directional sexual selection independently of female strain. However, laboratory females were less selective than wild ones. Additionally, correlational sexual selection was detected acting on the multivariate phenotype. The effects of correlational selection overlap with those of directional selection on each single trait. The analysis of mating pair characteristics showed patterns that do not match the expectations for a random mating system. The current analysis indicates that during mating pair formation two processes overlap. On the one hand, sexual selection favours males with larger size (TL) and narrower faces (FW). This effect occurs in both wild and laboratory females. In addition, assortative mating based on both phenotype and origin was also observed.
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Affiliation(s)
- M S Rodriguero
- Laboratorio de Genética de Poblaciones, Depto. Ecología, Genética y Evolución, Fac. Cs. Exactas y Naturales, Univ. Buenos Aires, (1428) Buenos Aires, Argentina
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Abstract
The uncoupling protein UCP1 is a member of a superfamily of homologous proteins formed by the mitochondrial metabolite transporters. Although they act in vivo as carriers, under specific experimental conditions some of these transporters have been shown to behave as channels. This dual transport operation suggests that these carriers are likely to be formed by two differentiated functional and structural domains. The kinetic model termed "single binding center gated pore" is well suited to understand the behaviour of these carriers. It proposes that in the protein core there must exist a hydrophilic translocation pore whose access is controlled by gates. It is highly likely that the hydrophilic channel is formed by the transmembrane alpha-helices and that loops contribute to the formation of the gates. UCP1 is regulated physiologically by fatty acids and purine nucleotides. Nucleotides maintain the proton conductance inhibited while fatty acids act as cytosolic second messengers of noradrenaline to active UCP1. Based on photoaffinity labeling and mutagenesis data, we propose a structural model for the localization of the binding site. The nucleotide enters through a gate in the cytosolic side and binds deep inside the protein. The three matrix loops contribute to the formation of a hydrophobic binding pocket that would accommodate the purine moiety. Three arginine residues (in helices II, IV, and VI) would interact with the phosphate groups. His214 and Glu190 have been involved in the pH regulation of the nucleotide binding but because they are on the cytosolic side of the protein, we propose that their state of protonation will determine the access of the nucleotide to the binding center.
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Affiliation(s)
- I Arechaga
- MRC-Dunn Human Nutrition Unit, Cambridge, United Kingdom
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Abstract
Brown fat is a thermogenic organ that allows newborns and small mammals to maintain a stable body temperature when exposed to cold. The heat generation capacity is based on the uncoupling of respiration from ATP synthesis mediated by the uncoupling protein UCP1. The first studies on the properties of these mitochondria revealed that fatty acid removal was an absolute prerequisite for respiratory control. Thus fatty acids, that are substrate for oxidation, were proposed as regulators of respiration. However, their ability to uncouple all types of mitochondria and the demonstration that several mitochondrial carriers catalyze the translocation of the fatty acid anion have made them unlikely candidates for a specific role in brown fat. Nevertheless, data strongly argue for a physiological function. First, fatty acids mimic the noradrenaline effects on adipocytes. Second, there exists a precise correlation between fatty acid sensitivity and the levels of UCP1. Finally, fatty acids increase the conductance by facilitating proton translocation, a mechanism that is distinct from the fatty acid uncoupling mediated by other mitochondrial carriers. The regulation of UCP1 and UCP2 by retinoids and the lack of effects of fatty acids on UCP2 or UCP3 are starting to set differences among the new uncoupling proteins.
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Affiliation(s)
- E Rial
- Centro de Investigaciones Biológicas, CSIC, Velázquez 144, 28006 Madrid, Spain.
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Rial E, González-Barroso M, Fleury C, Iturrizaga S, Sanchis D, Jiménez-Jiménez J, Ricquier D, Goubern M, Bouillaud F. Retinoids activate proton transport by the uncoupling proteins UCP1 and UCP2. EMBO J 1999; 18:5827-33. [PMID: 10545094 PMCID: PMC1171648 DOI: 10.1093/emboj/18.21.5827] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In mammalian brown adipose tissue, thermogenesis is explained by uncoupling mitochondrial respiration from ATP synthesis. Uncoupling protein-1 (UCP1) is responsible for this uncoupled state, because it allows proton re-entry into the matrix and thus dissipates the proton gradient generated by the respiratory chain. Proton transport by UCP1 is regulated negatively by nucleotides and positively by fatty acids. Adrenergic stimulation of brown adipocytes stimulates lipolysis and therefore enhances uncoupling and thermogenesis. Adrenergic stimulation also boosts ucp1 gene transcription. Since retinoic acid also promotes ucp1 gene transcription and its structure makes it a possible activator of UCP1, we hypothesized that retinoic acid, like noradrenaline, could have a dual action and trigger the activity of the protein UCP1 itself. Here we show that retinoic acid strongly increases proton transport by UCP1 in brown adipose tissue mitochondria and that it is much more potent than fatty acids. These data are corroborated with yeast mitochondria where UCP1 was introduced by genetic manipulation. The yeast expression system allows the comparison of the UCP1 with the newly described homologues UCP2 and UCP3. The search for regulators of UCP2 has demonstrated that it is positively regulated by retinoids in a pH-dependent manner.
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Affiliation(s)
- E Rial
- Centro Investigaciones Biologicas, CSIC, Velazquez 144, 28006 Madrid, Spain
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7
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Abstract
The lack of energy conservation in brown adipose tissue mitochondria when prepared by conventional methods was established in the 1960s and was correlated with the thermogenic function of the tissue. In order to observe energy conservation, two requirements had to be met: the removal of the endogenous fatty acids and the addition of a purine nucleotide. These two factors have been the essential tools that led to the discovery of the energy dissipation pathway, the uncoupling protein UCP1. The activity is regulated by these two ligands. Purine nucleotides bind from the cytosolic side of the protein and inhibit transport. Fatty acids act as seconds messengers of noradrenaline and increase the proton conductance. This review presents a historical perspective of the steps that led to the discovery of UCP1, its regulation, and our current view on its mechanism of transport.
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Affiliation(s)
- D G Nicholls
- Neurosciences Institute, Ninewells Medical School, Dundee University, Scotland
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González-Barroso MM, Fleury C, Jiménez MA, Sanz JM, Romero A, Bouillaud F, Rial E. Structural and functional study of a conserved region in the uncoupling protein UCP1: the three matrix loops are involved in the control of transport. J Mol Biol 1999; 292:137-49. [PMID: 10493863 DOI: 10.1006/jmbi.1999.3049] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It has been reported that the region 261-269 of the uncoupling protein from brown adipose tissue mitochondria, UCP1, has an important role in the control of its proton translocating activity. Thus the deletion of residues Phe267-Lys268-Gly269 leads to the loss of the nucleotide regulation of the protein, while the complete deletion of the segment leads to the formation of a pore. The region displays sequence homology with the DNA-binding domain of the estrogen receptor. The present report analyzes the structure, by NMR and circular dichroism, of a 20 amino acid residue peptide containing the residues of interest. We demonstrate that residues 263-268 adopt an alpha-helical structure. The helix is at the N-terminal end of the sixth transmembrane domain. The functional significance of this helix has been examined by site-directed mutagenesis of the protein expressed recombinantly in yeasts. Alterations in the structure or orientation of the region leads to an impairment of the regulation, by nucleotides and fatty acids, of the transport activity. UCP1 is one member of the family formed by the carriers of the mitochondrial inner membrane. The family is characterized by a tripartite structure with three repeated segments of about 100 amino acid residues. Two of the mutations have also been performed in the first and second matrix loops and the effect on UCP1 function is very similar. We conclude that the three matrix loops contribute to the formation of the gating domain in UCP1 and propose that they form a hydrophobic pocket that accommodates the purine moiety of the bound nucleotide.
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González-Barroso MM, Fleury C, Bouillaud F, Nicholls DG, Rial E. The uncoupling protein UCP1 does not increase the proton conductance of the inner mitochondrial membrane by functioning as a fatty acid anion transporter. J Biol Chem 1998; 273:15528-32. [PMID: 9624141 DOI: 10.1074/jbc.273.25.15528] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The activity of the brown fat uncoupling protein (UCP1) is regulated by purine nucleotides and fatty acids. Although the inhibition by nucleotides is well established, the activation by fatty acids is still controversial. It has been reported that the ADP/ATP carrier, and possibly other members of the mitochondrial carrier family, mediate fatty acid uncoupling of mitochondria from a variety of sources by facilitating the transbilayer movement of the fatty acid anion. Brown fat mitochondria are known to be more sensitive to fatty acid uncoupling, a property that has been assigned to the presence of UCP1. We have analyzed the transport properties of UCP1 and conclude that fatty acids are not essential for UCP1 function, although they increase its uncoupling activity. In order to establish the difference between the proposed carrier-mediated uncoupling and that exerted through UCP1, we have studied the facility with which fatty acids uncouple respiration in mitochondria from control yeast and strains expressing UCP1 or the mutant Cys-304 --> Gly. The concentration of free palmitate required for half-maximal activation of respiration in UCP1-expressing mitochondria is 80 or 40 nM for the mutant protein. These concentrations have virtually no effect on the respiration of mitochondria from control yeast and are nearly 3 orders of magnitude lower than those reported for carrier-mediated uncoupling. We propose that there exist two modes of fatty acid-mediated uncoupling; nanomolar concentrations activate proton transport through UCP1, but only if their concentrations rise to the micromolar range do they become substrates for nonspecific carrier-mediated uncoupling.
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Affiliation(s)
- M M González-Barroso
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, 28006 Madrid, Spain
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Alvarez-Fortes E, Ruiz-Pérez LM, Bouillaud F, Rial E, Rivas L. Expression and regulation of mitochondrial uncoupling protein 1 from brown adipose tissue in Leishmania major promastigotes. Mol Biochem Parasitol 1998; 93:191-202. [PMID: 9662704 DOI: 10.1016/s0166-6851(98)00029-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Rat uncoupling protein 1 (UCP1) was successfully translated in transfected Leishmania major promastigotes. Immune electron microscopy revealed that the protein was exclusively in the mitochondria. UCP1 expression was about 350,000 copies per promastigote, accounting for 4.7% of the total mitochondrial protein. In intact parasites, expression of UCP1 induced a slight increase in respiratory rate and a modest decrease in mitochondrial membrane potential (delta psi(m)). In contrast, in digitonin-permeabilized parasites, a significantly lower value both in delta psi(m) (57 +/- 10 vs 153 +/- 12 mV) and respiratory control ratio (0.99 vs 1.54) were observed for UCP1 versus control parasites, although when UCP1 activity was inhibited by bovine serum albumin (BSA) and GDP, control values were restored. Therefore, a fully functional UCP1 was present and only partially inhibited in vivo by endogenous purine nucleotides. However, neither ATP levels, growth rate nor mitochondrial protein import differed significantly between both types of parasites. Expression of the pore-like mutant UCP1 delta 9 was deleterious to the organism. Consequently, Leishmania was capable of expressing and importing into mitochondria proteins from higher eukaryotes lacking an N-terminal targeting pre-sequence as UCP1. As described previously, parasite metabolism had only a limited tolerance to mitochondrial disfunction. Transfection of Leishmania with foreign proteins which play an important regulatory role in metabolism is a useful tool to study both parasite metabolism in general, and alternative pathways involved in maintaining internal homeostasis.
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11
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Abstract
The uncoupling protein of brown adipose tissue (UCP1) is a transporter that allows the dissipation as heat of the proton gradient generated by the respiratory chain. The discovery of new UCPs in other mammalian tissues and even in plants suggests that the proton permeability of the mitochondrial inner membrane can be regulated and its control is exerted by specialised proteins. The UCP1 is regulated both at the gene and the mitochondrial level to ensure a high thermogenic capacity to the tissue. The members of the mitochondrial transporter family, which includes the UCPs, present two behaviours with carrier and channel transport modes. It has been proposed that this property reflects a functional organization in two domains: a channel and a gating domain. Mounting evidence suggest that the matrix loops contribute to the formation of the gating domain and thus they are determinants to the control of transport activity.
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Affiliation(s)
- E Rial
- Centro de Investigaciones Biológicas, C.S.I.C., Madrid, Spain.
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González-Barroso MM, Fleury C, Levi-Meyrueis C, Zaragoza P, Bouillaud F, Rial E. Deletion of amino acids 261-269 in the brown fat uncoupling protein converts the carrier into a pore. Biochemistry 1997; 36:10930-5. [PMID: 9283084 DOI: 10.1021/bi971104y] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The uncoupling protein (UCP) from brown adipose tissue mitochondria is a carrier that catalyzes proton re-entry into the matrix and thus dissipates the proton electrochemical potential gradient as heat. UCP activity is regulated: purine nucleotides inhibit while fatty acids activate transport. We have previously reported that sequence 261-269 of the UCP has a closely related counterpart in the adenine nucleotide translocator, as well as in the DNA binding domain of the estrogen receptor. Site-directed mutagenesis of the UCP showed that deletion of amino acids 267-269 in the UCP abolished nucleotide inhibition [Bouillaud, F., et al. (1994) EMBO J. 13, 1990-1997]. Complete deletion of the homologous domain (UCPDelta9) produced a highly deleterious mutant that collapsed the mitochondrial membrane potential and halted yeast growth. Since under our growth conditions revertants appeared rapidly, it was not possible to characterize this mutant. In this article, we have designed conditions to isolate mitochondria containing significant amounts of the UCPDelta9 mutant protein. These mitochondria show no respiratory control and are insensitive to nucleotides. Investigation of the permeability properties revealed that UCPDelta9 mitochondria swell rapidly in potassium salts in the absence of valinomycin, thus indicating a loss of specificity. The size exclusion properties of this mutant were determined with polyethylene glycols of various molecular masses (400-20000 Da), and it was found that UCPDelta9 can catalyze permeation of molecules of up to 1000 Da. We conclude that the deletion of amino acids 261-269 converts the UCP into an unspecific pore.
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Affiliation(s)
- M M González-Barroso
- Centro de Investigaciones Biológicas, CSIC, Madrid, Spain, and CEREMOD, CNRS, Meudon, France
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13
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Abstract
ATP lowers the efficiency of oxidative phosphorylation in Saccharomyces cerevisiae mitochondria by a mechanism that involves the activation of cytochrome c oxidase and the increase in anion permeability of the mitochondrial inner membrane (S. Prieto, F. Bouillaud, and E. Rial (1995) Biochem. J. 307, 657-661). In this study, we have carried out experiments to determine the transport specificity of the ATP-induced permeability pathway and its regulation. The pathway allows permeation of anions such as Cl- or Br- , while NO3-, N02-, or Tes are not transported. Transport is activated by ATP, GTP, dATP, dGTP, and GDP, while ADP, AMP, GMP, and pyrimidine nucleotides are ineffective. Analysis of transport inhibition by ADP and phosphate suggests that ADP is a competitive inhibitor of ATP while phosphate inhibition is noncompetitive. These effectors are operative in the physiological range of concentrations.
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Affiliation(s)
- S Prieto
- Centro de Investigaciones Biólogicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
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González-Barroso MM, Fleury C, Arechaga I, Zaragoza P, Levi-Meyrueis C, Raimbault S, Ricquier D, Bouillaud F, Rial E. Activation of the uncoupling protein by fatty acids is modulated by mutations in the C-terminal region of the protein. Eur J Biochem 1996; 239:445-50. [PMID: 8706753 DOI: 10.1111/j.1432-1033.1996.0445u.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The transport properties of the uncoupling protein (UCP) from brown adipose tissue have been studied in mutants where Cys304 has been replaced by either Gly, Ala, Ser, Thr, Ile or Trp. This position is only two residues away from the C-terminus of the protein, a region that faces the cytosolic side of the mitochondrial inner membrane. Mutant proteins have been expressed in Saccharomyces cerevisiae and their activity determined in situ by comparing yeast growth rates in the presence and absence of 2-bromopalmitate. Their bioenergetic properties have been studied in isolated mitochondria by determining the effects of fatty acids and nucleotides on the proton permeability and NADH oxidation rate. It is revealed that substitution of Cys304 by non-charged residues alters the response of UCP to fatty acids. The most effective substitution is Cys for Gly since it greatly enhances the sensitivity to palmitate, decreasing threefold the concentration required for half-maximal stimulation of respiration. The opposite extreme is the substitution by Ala which increases twofold the half-maximal concentration. We conclude that the C-terminal region participates in the fatty acid regulation of UCP activity. The observed correlation between yeast growth rates in the presence of bromopalmitate and the calculated activation constants for respiration in isolated mitochondria validates growth analysis as a method to screen the in situ activity of UCP mutants.
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Prieto S, Bouillaud F, Rial E. The mechanism for the ATP-induced uncoupling of respiration in mitochondria of the yeast Saccharomyces cerevisiae. Biochem J 1995; 307 ( Pt 3):657-61. [PMID: 7741693 PMCID: PMC1136701 DOI: 10.1042/bj3070657] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have recently reported that ATP induces an uncoupling pathway in Saccharomyces cerevisiae mitochondria [Prieto, Bouillaud, Ricquier and Rial (1992) Eur. J. Biochem. 208, 487-491]. The presence of this pathway would explain the reported low efficiency of oxidative phosphorylation in S. cerevisiae, and may represent one of the postulated energy-dissipating mechanisms present in these yeasts. In this paper we demonstrate that ATP exerts its action in two steps: first, at low ATP/Pi ratios, it increases the respiratory-chain activity, probably by altering the kinetic properties of cytochrome c oxidase. Second, at higher ATP/Pi ratios, an increase in membrane permeability leads to a collapse in membrane potential. The ATP effect on cytochrome c oxidase corroborates a recent report showing that ATP interacts specifically with yeast cytochrome oxidase, stimulating its activity [Taanman and Capaldi (1993) J. Biol. Chem. 268, 18754-18761].
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Affiliation(s)
- S Prieto
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
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Díaz-Achirica P, Prieto S, Ubach J, Andreu D, Rial E, Rivas L. Permeabilization of the mitochondrial inner membrane by short cecropin-A-melittin hybrid peptides. Eur J Biochem 1994; 224:257-63. [PMID: 8076647 DOI: 10.1111/j.1432-1033.1994.tb20019.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A number of cecropin-A-melittin hybrid peptides have previously been shown to be potent antibacterial agents [Andreu, D., Ubach, J., Boman, A., Wahlin, B., Wade, D., Merrifield, R. B. & Boman, H. G. (1992) FEBS Lett. 296, 190-194]. In the present report we analyze their action on biological systems using rat liver mitochondria as a test system. We demonstrate that the longest peptide, cecropin-A-(1-8)-melittin(1-18) permeabilizes the mitochondrial inner membrane allowing the movement of both charged and non-charged solutes. Concentrations used have already been shown to be bactericidal. This effect is also demonstrated under respiring conditions where succinate oxidation is uncoupled. Shorter analogs also permeabilize mitochondria although at ten-fold higher concentrations. Heparin potentiates the peptide effects at low concentrations, while at high concentration it becomes inhibitory. We propose that the cecropin-melittin analogs disrupt the mitochondrial membrane in a detergent-like mode rather than by creating selective channels as had been previously suggested.
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Affiliation(s)
- P Díaz-Achirica
- Centro de Investigaciones Biológicas, C.S.I.C., Madrid, Spain
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Bouillaud F, Arechaga I, Petit PX, Raimbault S, Levi-Meyrueis C, Casteilla L, Laurent M, Rial E, Ricquier D. A sequence related to a DNA recognition element is essential for the inhibition by nucleotides of proton transport through the mitochondrial uncoupling protein. EMBO J 1994; 13:1990-7. [PMID: 8168495 PMCID: PMC395041 DOI: 10.1002/j.1460-2075.1994.tb06468.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The uncoupling protein (UCP) is uniquely expressed in brown adipose tissue, which is a thermogenic organ of mammals. The UCP uncouples mitochondrial respiration from ATP production by introducing a proton conducting pathway through the mitochondrial inner membrane. The activity of the UCP is regulated: nucleotide binding to the UCP inhibits proton conductance whereas free fatty acids increase it. The similarities between the UCP, the ADP/ATP carrier and the DNA recognition element found in the DNA binding domain of the estrogen receptor suggested that these proteins could share common features in their respective interactions with free nucleotides or DNA, and thus defined a putative 'nucleotide recognition element' in the UCP. This article provides demonstration of the validity of this hypothesis. The putative nucleotide recognition element corresponding to the amino acids 261-269 of the UCP was gradually destroyed, and these mutant proteins were expressed in yeast. Flow cytometry, measuring the mitochondrial membrane potential in vivo, showed increased uncoupling activities of these mutant proteins, and was corroborated with studies with isolated mitochondria. The deletion of the three amino acids Phe267, Lys268 and Gly269, resulted in a mutant where proton leak could be activated by fatty acids but not inhibited by nucleotides.
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Affiliation(s)
- F Bouillaud
- Centre de Recherches sur l'Endocrinologie Moléculaire et le Développement, CNRS, Meudon, France
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Arechaga I, Raimbault S, Prieto S, Levi-Meyrueis C, Zaragoza P, Miroux B, Ricquier D, Bouillaud F, Rial E. Cysteine residues are not essential for uncoupling protein function. Biochem J 1993; 296 ( Pt 3):693-700. [PMID: 8280067 PMCID: PMC1137752 DOI: 10.1042/bj2960693] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The uncoupling protein (UCP) of brown adipose tissue is a regulated proton carrier which allows uncoupling of mitochondrial respiration from ATP synthesis and, therefore, dissipation of metabolic energy as heat. In this article we demonstrate that, when UCP is expressed in Saccharomyces cerevisiae, it retains all its functional properties: proton and chloride transport, high-affinity binding of nucleotides and regulation of proton conductance by nucleotides and fatty acids. Site-directed mutagenesis demonstrates that sequential replacement by serine of cysteine residues in the UCP does not affect either its uncoupling activity or its regulation by nucleotides and fatty acids, and therefore establishes that none of the seven cysteine residues present in the wild-type UCP is critical for its activity. These data indicate that transport models involving essential thiol groups can be discounted and that chemical modification data require critical re-evaluation.
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Affiliation(s)
- I Arechaga
- Centro de Investigaciones Biológicas, C.S.I.C., Madrid, Spain
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Viguera AR, Goñi FM, Rial E. The uncoupling protein from brown adipose tissue mitochondria. The environment of the tryptophan residues as revealed by quenching of the intrinsic fluorescence. Eur J Biochem 1992; 210:893-9. [PMID: 1483472 DOI: 10.1111/j.1432-1033.1992.tb17493.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The uncoupling protein from brown adipose tissue is a member of the family of metabolite carriers of the mitochondrial inner membrane. It contains two tryptophan residues which have been characterized by fluorescence spectroscopy. Application of fluorescence-quenching-resolved spectroscopy (FQRS) allowed the determination of the emission maximum for each residue, both of which occur at 332 nm, thus suggesting that they are both located in a non-polar environment. Fluorescence quenching has demonstrated that both residues are accessible to acrylamide and inaccessible to Cs+, while only one of them is accessible to I-. When FQRS is combined with guanidinium hydrochloride denaturation, the unfolding of the regions containing each tryptophan can be monitored separately as they are transferred to the polar medium where the emission maximum appears at 359 nm, revealing also that the iodide-accessible residue is more sensitive to the denaturant. Secondary structure predictions, together with the data presented here, suggest that the iodide-accessible residue could correspond to Trp173 and the denaturant-resistant iodide-inaccessible one to Trp280, located in the center of the sixth transmembrane alpha-helix. Interaction of the protein with GDP (a transport inhibitor) has been studied and has revealed that it partially shields Trp173 from the interaction with I-, as well as reducing the static component of the acrylamide quenching.
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Affiliation(s)
- A R Viguera
- Department of Biochemistry, University of the Basque Country, Bilbao, Spain
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Abstract
The growth of Saccharomyces cerevisiae cells under aerobic conditions, in the presence of an energy-rich source, leads to production of an excess of NAD(P)H. Since the redox balance must be maintained, it has been postulated that NAD(P)H reoxidation is accelerated by the activation of energy-dissipating reactions, which would, in turn, explain the low growth efficiencies observed. It has been demonstrated already in S. cerevisiae cultures that these putative energy-dissipating reactions are stimulated both by oxygen and high cytosolic ATP levels. In this paper, we show that ATP induces a proton-permeability pathway in mitochondria at concentrations which are within the physiological range, as revealed both from the ATP stimulation of respiration and from the induction of H(+)-dependent swelling. We also demonstrate that phosphate acts as a competitive inhibitor of the nucleotide, and since activation is observed even in the presence of atractylate, we postulate that the ATP-binding site is located in the outer face of the mitochondrial inner membrane.
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Affiliation(s)
- S Prieto
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
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Rial E, Muga A, Valpuesta JM, Arrondo JL, Goñi FM. Infrared spectroscopic studies of detergent-solubilized uncoupling protein from brown-adipose-tissue mitochondria. Eur J Biochem 1990; 188:83-9. [PMID: 2318205 DOI: 10.1111/j.1432-1033.1990.tb15374.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The uncoupling protein of brown-adipose-tissue mitochondria has been purified in the form of mixed micelles with lipid and reduced Triton X-100. This surfactant has the advantage over conventional Triton X-100, that it does not interfere with amide bands in infrared spectra. The structure of the uncoupling protein in micellar form has been examined by Fourier-transform infrared spectroscopy (FTIR). In order to decompose the amide I contour into its components, band-narrowing (Fourier derivation and deconvolution) and band-decomposition techniques have been used. Combining data from spectra taken in H2O and 2H2O media, the following percentage distribution of secondary structure patterns has been obtained: 50% alpha-helix, 28-30% beta-structure; 13-15% beta-turns and 7% unordered. Thermal denaturation of the uncoupling protein has also been monitored by FTIR. In accordance with previous observations of different proteins, thermal denaturation is marked by a shift in the amide I maximum and the appearance of two new peaks in 2H2O, at around 1620 cm-1 and 1685 cm-1. Denaturation occurs in the 40-50 degrees C temperature range, in agreement with studies of GDP-binding capacity. Cooling down the thermally denatured protein produces a new change in its secondary structure; however, the original conformation is not restored. The uncoupling protein possesses a nucleotide-binding site. On addition of GDP, small changes in protein conformation occur, attributable to changes in tertiary structure. However, no detectable effects are seen in the presence or absence of the other physiological regulators, the free fatty acids. The uncoupling protein shares important similarities in its primary structure with other anion carriers of the mitochondrial membrane; one of these, the adenine-nucleotide translocator, has been used in a comparative study, applying the same FTIR techniques described above for the uncoupling protein. Both proteins have a similar proportion of alpha-helix, probably corresponding to the segments spanning the membrane, but the conformation of the polar domains appears to differ.
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Affiliation(s)
- E Rial
- Department of Biochemistry, Faculty of Science, University of the Basque Country, Bilbao, Spain
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Rial E, Aréchaga I, Sainz-de-la-Maza E, Nicholls DG. Effect of hydrophobic sulphydryl reagents on the uncoupling protein and inner-membrane anion channel of brown-adipose-tissue mitochondria. Eur J Biochem 1989; 182:187-93. [PMID: 2471645 DOI: 10.1111/j.1432-1033.1989.tb14816.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The effects of three sulphydryl reagents of differing hydrophobicity (N-ethylmaleimide, N-benzylmaleimide and N,N'-o-phenylenedimaleimide) on ion permeation through the inner membrane of brown-adipose-tissue mitochondria are investigated. GDP-sensitive permeation of chloride and protons (hydroxyl ions) through the uncoupling protein is increased exponentially with time by all three reagents. With increasing hydrophobicity of the reagents, modification is enhanced and an initial inhibited state becomes apparent. Results are interpreted in terms of a two-stage modification via a non-transporting intermediate, which does not bind GDP, to a final highly conducting product. The reagents also react with a hydrophilic sulphydryl group on an independent protein to induce a GDP-insensitive pathway which allows chloride, phosphate and sulphate to cross the membrane. The use of different sulphydryl reagents allows the two pathways to be clearly distinguished.
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Affiliation(s)
- E Rial
- Department of Biochemistry, Dundee University
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Fernández M, Nicholls DG, Rial E. The uncoupling protein from brown-adipose-tissue mitochondria. Chymotrypsin-induced structural and functional modifications. Eur J Biochem 1987; 164:675-80. [PMID: 3569282 DOI: 10.1111/j.1432-1033.1987.tb11179.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Mitoplasts prepared from brown adipose tissue mitochondria were treated with chymotrypsin and the fragments derived from the 32-kDa uncoupling protein identified by immunoblotting. Extensive proteolysis of the uncoupling protein occurred, the polypeptide pattern being affected by binding of the inhibitory nucleotide GDP. Chymotrypsin modifies the nucleotide binding site, lowering its affinity from 1.7 microM to 21 microM but without decreasing its binding capacity. Nucleotide bound to the modified site can still inhibit the permeation of H+ and Cl- through the protein. The ion conducting pathway itself is also sensitive to chymotrypsin, Cl- and H+ transport being partially inhibited in parallel. The ability of fatty acids to increase the H+ permeability of the protein is also inhibited in parallel with the basal H+ permeability. The results confirm that the transport of H+ and Cl-, and the fatty acid regulation of H+ permeation all share a common structural element within the 32-kDa protein.
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Rial E, Nicholls DG. Chemical modification of the brown-fat-mitochondrial uncoupling protein with tetranitromethane and N-ethylmaleimide. A cysteine residue is implicated in the nucleotide regulation of anion permeability. Eur J Biochem 1986; 161:689-94. [PMID: 3024980 DOI: 10.1111/j.1432-1033.1986.tb10494.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Treatment of brown adipose tissue mitochondria with tetranitromethane or N-ethylmaleimide decreases the affinity with which inhibitory nucleotide GDP binds to the tissue-specific uncoupling protein. Both reagents modify cysteine residues which are 'accessible' and 'buried' to 5,5'-dithio-bis(2-nitrobenzoic acid) (Nbs2). Modification of the single Nbs2-accessible residue correlates with the loss of high-affinity binding sites for GDP. Tetranitromethane does not affect the Cl- or H+ permeability of the protein in the absence of nucleotide, while N-ethylmaleimide increases both by 70-80%. Bound GDP is a less effective inhibitor of Cl- permeability after N-ethylmaleimide or tetranitromethane treatment, but retains much of the ability to inhibit H+ permeation.
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Abstract
Tetranitromethane reacts with the uncoupling protein of intact brown fat mitochondria. The chloride permeability in the absence of the inhibitory nucleotide GDP is not affected, but the affinity with which GDP binds is decreased, and the coupling between binding of nucleotide and inhibition of chloride permeation is broken.
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Cunningham S, Leslie P, Hopwood D, Illingworth P, Jung RT, Nicholls DG, Peden N, Rafael J, Rial E. The characterization and energetic potential of brown adipose tissue in man. Clin Sci (Lond) 1985; 69:343-8. [PMID: 2998687 DOI: 10.1042/cs0690343] [Citation(s) in RCA: 74] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In adult man, brown fat can be detected in perinephric fat depots by visual inspection, electron microscopy and nucleotide binding to the tissue-specific uncoupling protein. The 32 kDa uncoupling protein is functionally active, showing a nucleotide-sensitive conductance to protons and an uncoupling response to fatty acids. The amount of uncoupling protein in human mitochondria is equivalent to that in a partially cold-adapted guinea pig, indicating some potential for thermogenesis. Respiratory capacity measurements indicate that the total perinephric fat in adult man can only account for one-fivehundredth of the whole-body response to infused noradrenaline. Thus, although brown fat has been found to be quantitatively important in animal studies, considerable caution must be exercised in extrapolating its significance to adult man.
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Rial E, Nicholls DG. The mitochondrial uncoupling protein from guinea-pig brown adipose tissue. Synchronous increase in structural and functional parameters during cold-adaptation. Biochem J 1984; 222:685-93. [PMID: 6091621 PMCID: PMC1144231 DOI: 10.1042/bj2220685] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The time-course for the induction of the uncoupling pathway in the inner membrane of brown-fat mitochondria from cold-adapting guinea pigs was studied. The amount of the protein was quantified from the capacity for high-affinity binding of GDP to the intact mitochondria, and was compared with the functional parameters diagnostic of the protein, namely the nucleotide-sensitive proton conductance and the sensitivity to uncoupling by low concentrations of fatty acids. A monophasic increase in nucleotide titre was observed, with no evidence of an early 'unmasking' of preexisting nucleotide-binding sites. The nucleotide-sensitive conductance increased in precise synchrony with the nucleotide-binding capacity. Mitochondria from newborn animals, and those from acutely cold-adapted animals, showed anomalously low sensitivities to uncoupling by fatty acids.
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Goñi FM, Valpuesta JM, Barbero MC, Rial E, Gurtubay JI, Macarulla JM. Physiological state of submitochondrial particles and their susceptibility to Triton X-100. Experientia 1984; 40:193-5. [PMID: 6698174 DOI: 10.1007/bf01963595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The solubilizing effect of Triton X-100 on beef heart submitochondrial particles (ETPH) has been studied under various physiological conditions. Coupled, uncoupled and azide-inhibited ETPH particles have been studied. Quantitative and qualitative differences are found in the proteins solubilized by the detergent from ETPH particles under the various conditions tested.
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Barbero MC, Valpuesta JM, Rial E, Gurtubay JI, Goñi FM, Macarulla JM. Effect of the nonionic detergent Triton X-100 on mitochondrial succinate-oxidizing enzymes. Arch Biochem Biophys 1984; 228:560-8. [PMID: 6320742 DOI: 10.1016/0003-9861(84)90023-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Specific activities of succinate:coenzyme Q reductase, ubiquinone:cytochrome c reductase, cytochrome oxidase, succinate:cytochrome c reductase, succinate oxidase, and ubiquinol oxidase have been measured in rat liver mitochondria in the presence of Triton X-100. The last three activities are much more sensitive to Triton X-100 than the first ones; the data suggest that the electron transport chain components cannot react with each other in the presence of the detergent. At least in the case of succinate:cytochrome c reductase, reconstitution of the detergent-treated membranes with externally added phospholipids reverses the inhibition produced by Triton X-100. These results support the idea that the respiratory chain components diffuse at random in the plane of the inner mitochondrial membrane; the main effect of the detergent would be to impair lateral diffusion by decreasing the area of lipid bilayer. When detergent-treated mitochondrial suspensions are centrifuged in order to separate the solubilized from the particulate material, only the first three enzyme activities mentioned above are found in the supernatants. After centrifugation, a latent ubiquinol:cytochrome c oxidase activity becomes apparent, whereas the same centrifugation process produces inhibition of cytochrome c oxidase in the presence of certain Triton X-100 concentrations. These effects could be due either to a selective solubilization of regulatory or catalytic subunits or to a conformational change of the enzyme-detergent complex.
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Rial E, Poustie A, Nicholls DG. Brown-adipose-tissue mitochondria: the regulation of the 32000-Mr uncoupling protein by fatty acids and purine nucleotides. Eur J Biochem 1983; 137:197-203. [PMID: 6317384 DOI: 10.1111/j.1432-1033.1983.tb07815.x] [Citation(s) in RCA: 139] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The increased proton permeability induced by the addition of a synthetic proton translocator to non-respiring hamster brown-fat mitochondria is unaffected by purine nucleotide addition. In contrast the permeability induced by fatty acids is inhibited by nucleotide, indicating that fatty acids act at the 32000-Mr uncoupling protein. Fatty acids lower the affinity of nucleotide binding to the 32000-Mr protein, but not sufficiently to explain their uncoupling action. The sensitivity of the fatty acid modulation of permeability is dependent on chain length, extent of unsaturation and pH. There is a requirement for an unesterified carboxyl group. In respiring mitochondria fatty acids act in the presence of nucleotide by lowering the 'break-point' potential at which the conductance of the 32000-Mr protein increases. Fatty acids have no effect on the chloride uniport activity of the 32000-Mr protein, but decouple the interference between chloride and protons when the simultaneous transport of both ions is attempted.
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Rial E, Nicholls DG. The regulation of the proton conductance of brown fat mitochondria. Identification of functional and non-functional nucleotide-binding sites. FEBS Lett 1983; 161:284-8. [PMID: 6311625 DOI: 10.1016/0014-5793(83)81026-6] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The binding of purine nucleotides to intact brown fat mitochondria is re-examined. In addition to the previously reported high affinity binding site, a low-affinity site is found, which requires several minutes to saturate. Only the high affinity site is functional in regulating the proton and halide permeabilities of the mitochondria. The low affinity site can introduce errors in the use of nucleotide binding to quantitate the Mr 32000 uncoupling protein unique to these mitochondria.
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Locke RM, Rial E, Nicholls DG. The acute regulation of mitochondrial proton conductance in cells and mitochondria from the brown fat of cold-adapted and warm-adapted guinea pigs. Eur J Biochem 1982; 129:381-7. [PMID: 6295766 DOI: 10.1111/j.1432-1033.1982.tb07061.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Cells and mitochondria were prepared from the brown adipose tissue of adult guinea-pigs adapted to either 4-7 degrees C or 22-25 degrees C. The cold-adapted cells displayed noradrenaline-stimulated, propranolol-sensitive respiration, but noradrenaline failed to increase the respiration of the warm-adapted cells. Purine-nucleotide-sensitive proton conductance was greater in cold-adapted mitochondria than in warm-adapted controls. At the same time cold-adapted mitochondria were extremely sensitive to the uncoupling effect of endogenous and infused fatty acids, and resembled the mitochondria from the brown adipose tissue of cold-adapted hamsters. Warm-adapted mitochondria were ninefold less sensitive, and resembled liver mitochondria. With cold-adapted, but not warm-adapted mitochondria, respiration increased proportionately to the rate of fatty acid infusion. It is concluded that the presence of the 32000-Mr proton conductance pathway is necessary for the expression of a high sensitivity to fatty acid uncoupling, suggesting that the fatty acids interact directly with this protein to modulate the proton conductance during the acute regulation of thermogenesis.
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Locke RM, Rial E, Scott ID, Nicholls DG. Fatty acids as acute regulators of the proton conductance of hamster brown-fat mitochondria. Eur J Biochem 1982; 129:373-80. [PMID: 6295765 DOI: 10.1111/j.1432-1033.1982.tb07060.x] [Citation(s) in RCA: 107] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Possible mechanisms are evaluated for the acute regulation of the hamster brown-fat mitochondrial proton-conductance pathway which is active during non-shivering thermogenesis. Isolated mitochondria are incubated under conditions designed to approximate to the non-thermogenic state, and the effect of the steady infusion of fatty acids or acyl derivatives upon respiration, membrane potential and membrane proton conductance is monitored continuously. Fatty acids increase the proton conductance with no detectable threshold concentration, allowing the generated acyl carnitine to be rapidly oxidized. The extent of depolarization and of respiratory increase is a function of the rate of infusion. Immediately infusion is terminated the conductance decreases, the mitochondria repolarize and respiration returns to the initial rate. Infusion of acyl-CoA and acylcarnitine cause only a slight depolarization or respiratory increase after high concentrations of these derivatives have accumulated. Any factor which decreases the rate of conversion of fatty acid to acyl-CoA potentiates the conductance increase. An effect of acyl-CoA upon chloride permeability is not specific to brown-fat mitochondria. Fatty acids infused into rat liver mitochondrial incubations produced a small conductance increase, comparable to that of acyl-CoA or acylcarnitine. It is concluded that fatty acids are the most plausible acute regulators of the proton conductance. The relation to the brown-fat-specific 32000-Mr protein is discussed.
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Barbero MC, Rial E, Otamendi JJ, Gurtubay JI, Goñi FM. Fractionation of rat liver mitochondrial components after short treatments with Triton X-100. Int J Biochem 1982; 14:933-40. [PMID: 7128910 DOI: 10.1016/0020-711x(82)90078-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
1. When rat liver mitochondria are treated with the non-ionic detergent Triton X-100, the solubilizing effects of the latter are already maximal after a few seconds. 2. We have developed a filtration technique that allows a fast separation of the solubilized and non-solubilized fractions. By means of this technique, we have been able to show differences in the solubilizing effect of Triton X-100 according to the physiological state of mitochondria. 3. In addition, the filtrate may be subjected to further fractionation by ultracentrifugation, by which two filtrate subfractions, supernatant and pellet, may be obtained. 4. Filtrates, supernatants and pellets differ from each other, and from intact mitochondria, in phospholipid and polypeptide composition, and possess a characteristic distribution of enzyme activities; they are also different from the ultrastructural point of view. 5. It is concluded that the combined techniques of short detergent treatments and fast filtration are useful in structural and functional studies of mitochondria and in the selective solubilization of mitochondrial components.
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Barbero MC, Romay J, Rial E, Gurtubay JI, Goñi FM. Protein assay of rat liver mitochondria and mitochondrial membrane preparations. Rev Esp Fisiol 1981; 37:353-8. [PMID: 7323398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Alonso A, Prado A, Rial E, Sáez R, Valpuesta JM. Constancy of liver lipid composition in two genera of toads after a short-term temperature acclimation. Rev Esp Fisiol 1981; 37:57-64. [PMID: 7244328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The lipid and fatty acid composition of Bufo calamytes and Alytes obstetricans livers has been studied. Data for both species are similar, and resemble closely those published for Rana sculenta. Total lipids constitute 20-25% of the total liver dry weight; about one fifth of these are phospholipids; cholesterol makes up 1.7-2.2% of the total liver dry weight. The most abundant phospholipids are phosphatidylcholine and phosphatidylethanolamine. The various lipid cases differ in their fatty acid composition: neutral lipids contain high proportions of palmitoleic and linoleic acids; phosphatidylcholine is characterized by its contents in palmitic acid, whereas cardiolipin contains polyunsaturated fatty acids. Thermal acclimation of toads for 96 h produces but few changes in liver lipid composition.
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Barbero MC, Prado A, Rial E, Saez R, Valpuesta JM. Lipids of marine teleost fish (Teleostei). Biochem Soc Trans 1980; 8:547-8. [PMID: 7450216 DOI: 10.1042/bst0080547a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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