TY  - JOUR
AB  - The presence of two distinct types of adipose tissue, which have opposing functions, has been known for decades. White adipose tissue (WAT) is the main tissue of energy storage, while brown adipose tissue (BAT) dissipates energy as heat and is required for non-shivering thermoregulation. In the last few years, a third type of adipocyte was identified, termed the brite ("brown and white") or beige adipocyte. Their physiological control and role, however, is not fully clarified. Brite/beige adipocytes have a positive impact on systemic metabolism that is generally explained by thermogenesis of brite/beige adipocytes; although thermogenesis has not been directly measured but is mostly inferred by gene expression data of typical thermogenic genes such as uncoupling protein 1 (UCP1). Here we critically review functional evidence for the thermogenic potential of brite/beige adipocytes, leading to the conclusion that direct measurements of brite/beige adipocyte bioenergetics, beyond gene regulation, are pivotal to quantify their thermogenic potential. In particular, we exemplified that the massive induction of UCP1 mRNA during browning of isolated subcutaneous adipocytes in vitro is not reflected in significant alterations of cellular bioenergetics. Herein, we demonstrate that increases in mitochondrial respiration in response to beta-adrenergic stimulus can be independent of UCP1. Using HEK293 cells expressing UCP1, we show how to directly assess UCP1 function by adequate activation in intact cells. Finally, we provide a guide on the interpretation of UCP1 activity and the pitfalls by solely using respiration measurements. The functional analysis of beige adipocyte bioenergetics will assist to delineate the impact of browning on thermogenesis, possibly elucidating additional physiological roles and its contribution to systemic metabolism, highlighting possible avenues for future research.
AU  - Keipert, S.
AU  - Jastroch, M.
C1  - 30583
C2  - 33737
CY  - Amsterdam
SP  - 1075-1082
TI  - Brite/beige fat and UCP1 - is it thermogenesis?
JO  - Biochim. Biophys. Acta-Bioenerg.
VL  - 1837
IS  - 7
PB  - Elsevier Science Bv
PY  - 2014
SN  - 0005-2728
ER  - 

TY  - JOUR
AB  - Mechanistic studies on uncoupling proteins (UCPs) not only are important to identify their cellular function but also are pivotal to identify potential drug targets to manipulate mitochondrial energy transduction. So far, functional and comparative studies of uncoupling proteins in their native environment are hampered by different mitochondrial, cellular and genetic backgrounds. Artificial systems such as yeast ectopically expressing UCPs or liposomes with reconstituted UCPs were employed to address crucial mechanistic questions but these systems also produced inconsistencies with results from native mitochondria. We here introduce a novel mammalian cell culture system (Human Embryonic Kidney 293 - HEK293) to study UCP1 function. Stably transfected HEK293 cell lines were derived that contain mouse UCP1 at concentrations comparable to tissue mitochondria. In this cell-based test system UCP1 displays native functional behaviour as it can be activated with fatty acids (palmitate) and inhibited with purine nucleotides guanosine-diphosphate (GDP). The catalytic centre activity of the UCP1 homodimer in HEK293 is comparable to activities in brown adipose tissue supporting functionality of UCP1. Importantly, at higher protein levels than in yeast mitochondria, UCP1 in HEK293 cell mitochondria is fully inhibitable and does not contribute to basal proton conductance, thereby emphasizing the requirement of UCP1 activation for therapeutic purposes. These findings and resulting analysis on UCP1 characteristics demonstrate that the mammalian HEK293 cell system is suitable for mechanistic and comparative functional studies on UCPs and provides a non-confounding mitochondrial, cellular and genetic background.
AU  - Jastroch, M.
AU  - Hirschberg, V.*
AU  - Klingenspor, M.*
C1  - 8308
C2  - 30105
SP  - 1660-1670
TI  - Functional characterization of UCP1 in mammalian HEK293 cells excludes mitochondrial uncoupling artefacts and reveals no contribution to basal proton leak.
JO  - Biochim. Biophys. Acta-Bioenerg.
VL  - 1817
IS  - 9
PB  - Elsevier
PY  - 2012
SN  - 0005-2728
ER  - 

TY  - JOUR
AB  - The Tim23 protein is the key component of the mitochondrial import machinery. It locates to the inner mitochondrial membrane and its own import is dependent on the DDP1/TIM13 complex. Mutations in human DDP1 cause the Mohr-Tranebjaerg syndrome (MTS/DFN-1; OMIM #304700), which is one of the two known human diseases of the mitochondrial protein import machinery. We created a Tim23 knockout mouse from a gene trap embryonic stem cell clone. Homozygous Tim23 mice were not viable. Heterozygous F1 mutants showed a 50% reduction of Tim23 protein in Western blot, a neurological phenotype and a markedly reduced life span. Haploinsufficiency of the Tim23 mutation underlines the critical role of the mitochondrial import machinery for maintaining mitochondrial function.
AU  - Ahting, U.
AU  - Floß, T.
AU  - Uez, N.
AU  - Schneider-Lohmar, I.
AU  - Becker, L.
AU  - Kling, E.
AU  - Iuso, A.
AU  - Bender, A.*
AU  - Hrabě de Angelis, M.
AU  - Gailus-Durner, V.
AU  - Fuchs, H.
AU  - Meitinger, T.
AU  - Wurst, W.
AU  - Prokisch, H.
AU  - Klopstock, T.
C1  - 5077
C2  - 25891
SP  - 371-376
TI  - Neurological phenotype and reduced lifespan in heterozygous Tim23 knockout mice, the first mouse model of defective mitochondrial import.
JO  - Biochim. Biophys. Acta-Bioenerg.
VL  - 1787
IS  - 5
PB  - Elsevier
PY  - 2009
SN  - 0005-2728
ER  - 

TY  - JOUR
AB  - The yeast orthologue of mammalian TCTP is here proposed to be named Mmi1p (microtubule and mitochondria interacting protein). This protein displays about 50% amino acid sequence identity with its most distantly related orthologs in higher organisms and therefore probably belongs to a small class of yeast proteins which have housekeeping but so far incompletely known functions needed for every eukaryotic cell. Previous investigations of the protein in both higher cells and yeast revealed that it is highly expressed during active growth, but transcriptionally down-regulated in several kinds of stress situations including starvation stress. In human cells, TCTP presumably has anti-apoptotic functions as it binds to Bcl-XL in vivo. TCTP of higher cells was also shown to interact with the translational machinery. It has acquired an additional function in the mammalian immune system, as it is identical with the histamine releasing factor. Here, we show that in S. cerevisiae induction of apoptosis by mild oxidative stress, replicative ageing or mutation of cdc48 leads to translocation of Mmi1p from the cytoplasm to the mitochondria. Mmi1p is stably but reversibly attached to the outer surface of the mitochondria and can be removed by digestion with proteinase K. Glutathionylation of Mmi1p, which is also induced by oxidants, is not a prerequisite or signal for translocation as shown by replacing the only cysteine of Mmi1p by serine. Mmi1p probably interacts with yeast microtubules as deletion of the gene confers sensitivity to benomyl. Conversely, the deletion mutant displays resistance to hydrogen peroxide stress and shows a small but significant elongation of the mother cell-specific lifespan. Our results so far indicate that Mmi1p is one of the few proteins establishing a functional link between microtubules and mitochondria which may be needed for correct localization of mitochondria during cell division.
AU  - Rinnerthaler, M.*
AU  - Jarolim, S.*
AU  - Heeren, G.*
AU  - Palle, E.*
AU  - Perju, S.*
AU  - Klinger, H.*
AU  - Bogengruber, E.*
AU  - Madeo, F.*
AU  - Braun, R.J.
AU  - Breitenbach-Koller, L.*
AU  - Breitenbach, M.*
AU  - Laun, P.*
C1  - 5234
C2  - 24667
SP  - 631-638
TI  - MMI1 (YKL056c, TMA19), the yeast orthologue of the translationally controlled tumor protein (TCTP) has apoptotic functions and interacts with both microtubules and mitochondria.
JO  - Biochim. Biophys. Acta-Bioenerg.
VL  - 1757
IS  - 5-6
PB  - Elsevier
PY  - 2006
SN  - 0005-2728
ER  - 

TY  - JOUR
AB  - Polyamines have been described to protect against numerous oxidative stresses in plants. Increasing UV-B radiation (280–315 nm) in the biosphere may also induce an increase in radical formation in tissues. This study employed the tobacco cultivars Bel B and Bel W3 to describe possible protective functions of polyamines against UV-B radiation in sun light simulators (GSF/Munich) with natural diurnal fluctuations of simulated UV-B. Polyamine measurements on a whole leaf basis in isolated chloroplasts and thylakoids were paralleled to photosynthetic and respiration rates, photosynthetic efficiency, leaf thickness and photosynthetic pigment compositions. The study revealed that an increase of polyamines, and especially of putrescine level in thylakoid membranes upon elevated UV-B exposure comprises one of the primary protective mechanisms in the photosynthetic apparatus of the tobacco variety Bel B against UV-B radiation. The tobacco cultivar Bel W3, sensitive to ozone, was also proved to be sensitive to UV-B. This sensitivity is attributed to its incapability to enhance putrescine level in thylakoid membranes. After prolongation of UV-B exposure, when endogenous plant balances are being gradually restored, due to secondary responses, (e.g., biosynthesis of carotenoids and of additional flavonoids) and the plant is adapting to the altered environmental conditions, then the polyamine level is being reduced. Thus, we can discriminate the UV-B induced stress period from a UV-B acclimation period.
AU  - Lütz, C.*
AU  - Navakoudis, E.*
AU  - Seidlitz, H.K.
AU  - Kotzabasis, K.*
C1  - 1005
C2  - 23074
SP  - 24-33
TI  - Simulated solar irradiation with enhanced UV-B adjust plastid- and thylakoid-associated polyamine changes for UV-B protection.
JO  - Biochim. Biophys. Acta-Bioenerg.
VL  - 1710
IS  - 1
PY  - 2005
SN  - 0005-2728
ER  - 

TY  - JOUR
AB  - The pools of ribonucleoside di- and triphosphates decrease within a few min after addition of 5 mM sulfite to a suspension of Saccharomyces cerevisiae at pH 3.6. Levels of the corresponding ribonucleoside monophosphates increase in parallel. The strongest effect was observed with the adenosine phosphate pools. Depletion of ATP by sulfite at pH 3.6 occurs both in the presence and absence of glucose. These findings point to at least two different mechanisms for sulfite action on energy metabolism. Glycolysis is effectively impaired by low sulfite concentrations. The enzymes glyceraldehyde-3-phosphate dehydrogenase and alcohol dehydrogenase are inhibited by sulfite in vitro. In addition, formation of adducts between sulfite and aldehydes contributes to the inhibition of enzymatic reactions as shown with alcohol dehydrogenase. Sulfite also causes reduction of oxygen consumption of glucose-starved yeast at pH 3.6 which coincides with ATP depletion. In vitro, the oligomycin-sensitive F1-ATPase of yeast is stimulated 2.8-fold by 1 mM sulfite at pH 5.7. However, this stimulation does not seem to be involved in sulfite-initiated ATP depletion as concluded from experiments with the F1-ATPase-deficient mutant pet 936. At pH 3.6, the intracellular proton concentration of yeast is increased from 3.2-6.3·10-8 M to 4.0·10-6 M by 1 mM sulfite. In spite of the marked intracellular acidification, stimulation of an ATP-driven proton pump is not the chief cause for the sulfite-initiated ATP decrease. During short exposure of yeast to sulfite the effect on energy metabolism is reversible.
AU  - Maier, K.L.
AU  - Hinze, H.
AU  - Leuschel, L.
C1  - 41709
C2  - 38378
SP  - 120-130
TI  - Mechanism of sulfite action on the energy metabolism of Saccharomyces cerevisiae.
JO  - Biochim. Biophys. Acta-Bioenerg.
VL  - 848
IS  - 1
PY  - 1986
SN  - 0005-2728
ER  - 

TY  - JOUR
AB  - Cytochrome c-551.5 of the anaerobic sulfur-reducing bacterium Desulfuromonas acetoxidans has been purified to homogeneity and characterized. It elicits absorption bands at 551.5, 522.5 and 418 nm in the reduced form; the absorptivity ratio Aα(red) A280 nm (ox) equals 3.8 for the pure preparation. The molecular weight was estimated to be 9800 by gel filtration. Determination of the amino acid composition and analysis of the N-terminal amino acid sequence showed the cytochrome to be identical with the threehaem cytochrome c-551.5 (c7) isolated from the syntrophic mixed culture Chloropseudomonas ethylica strain 2K. The occurrence of multihaem cytochromes c in bacteria is discussed.
AU  - Probst, I.
AU  - Bruschi, M.H.*
AU  - PFENNIG, N.
AU  - Le Gall, J.Y.*
C1  - 40946
C2  - 38288
SP  - 58-64
TI  - Cytochrome c-551.5 (c7) from Desulfuromonas acetoxidans.
JO  - Biochim. Biophys. Acta-Bioenerg.
VL  - 460
IS  - 1
PY  - 1977
SN  - 0005-2728
ER  -