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PubMed1990

Expression of the brown fat mitochondria uncoupling protein in Xenopus oocytes and important into mitochondrial membrane.

Non shivering thermogenesis of brown adipose tissue is due to the uncoupling protein (UCP), located in the inner mitochondrial membrane, which functions as a proton translocator and can thus uncouple mitochondrial respiration. We describe here the expression of UCP in Xenopus laevis oocytes after injection of UCP mRNA, which was transcribed in vitro. UCP seems to be correctly transported into mitochondria and integrated into the membrane, but we were not able to establish definitely the functionality of this UCP. We conclude that this expression system could be suitable for the study of the mitochondrial import mechanism but not for the examination of physiological properties of UCP.

Adipose Tissue, Brown↗
PubMed1991

Calcium modulation of mitochondrial inner membrane channel activity.

Protocols were defined that enable patch-clamp studies of the approximately 107 pS voltage dependent channel and a class of activity we refer to as MCC (multiconductance channel) which is characterized by multiple levels and transitions as high as 1 to 1.5 nS. If free calcium was kept at 10(-7) M or lower during mitochondrial isolation, no activity was observed at low voltage (+/- 60 mV). If free calcium levels were higher, MCC activity was observed in about 96% of the patches. The observation of approximately 107 pS channel was enhanced from 2% to 68% of patches by washing isolated mitoplasts (mitochondria stripped of outer membrane) with EGTA. Increasing matrix calcium from 10(-9) to 10(-5) M decreased the probability of opening for the MCC and approximately 107 pS activities.

Animals↗
PubMed1992

Electron transport between cytochrome c and alpha tocopherol.

Using liposomes we have demonstrated an electron transfer between tocopherol (vitamin E) and cytochrome c. Reduced cytochrome c protects vitamin E from oxidation induced either directly by ultraviolet light or indirectly by soybean lipoxygenase-catalyzed oxidation of arachidonic acid. Oxidized cytochrome c is reduced by tocopherol and tocopherol homologues (chromanols) resulting in accumulation of tocopheroxyl radicals which we detected by ESR. The peak height of the ESR spectrum of tocopheroxyl radicals (which is proportional to the amount of radical present) is proportional to the ratio of reduced to oxidized cytochrome c. In mitochondrial membranes succinate-cytochrome c reduction is inhibited by antimycin A. Addition of exogenous chromanols facilitates a by-pass of the antimycin A blocked electron pathway, and succinate-dependent cytochrome c reductase activity is restored. Cytochrome c may act as a water-soluble complement to the lipid-soluble ubiquinol in regenerating mitochondrial tocopherol from tocopheroxyl radical.

Animals↗
PubMed1988

Pethidine analogues, a novel class of potent inhibitors of mitochondrial NADH: ubiquinone reductase.

Analogues of the analgetic drug pethidine were synthesized. Two N-aralkylen derivatives displayed a superior inhibitory effect on the activity of NADH:ubiquinone reductase in beef heart mitochondrial membranes. Dose-response curves revealed that the potency of these compounds is very comparable to that of the standard probe rotenone. The inhibitors were characterized by (a) their action on the reductase activity in various (eukaryotic and prokaryotic) organisms, (b) their influence on the enzyme kinetics, (c) their effects on the NADH dependent reduction of different electron acceptors, (d) their interference with the activities of other mitochondrial oxido-reductases. With regard to many of these aspects a close analogy between pethidine derivatives and rotenone was observed. A computer simulation of the steric structures of these molecules indicates that both classes of the chemically rather unrelated inhibitors may imitate very similar conformations. The potential advantages of the pethidine derivatives for the investigation of structure - function relationships within complex I of the respiratory chain is discussed.

Animals↗
PubMed1989

Photoaffinity labelling of mitochondrial NADH: ubiquinone reductase with pethidine analogues.

1. Chemically reactive derivatives of pethidine analogues--novel potent inhibitors of the mitochondrial NADH: ubiquinone reductase (complex I)--were synthesized. 2. Dose-response curves of these components revealed that the photoactivatable aryl azido derivative has retained most of the inhibitory activity displayed by the parent substance. After introduction of a radioactive iodine isotope into the molecule, it was used as a probe for the localization of the inhibitor binding polypeptides within complex I. 3. Photolysis of the radiolabelled derivative bound to isolated complex I both from Neurospora crassa and beef heart resulted in a covalent incorporation of the inhibitor into 6-7 individual subunits of the enzyme. Essentially the same labelling patterns were obtained, when whole mitochondrial membranes were incubated with the reactive derivative. 4. Applying a double isotope labelling technique, the inhibitor-binding polypeptides in N. crassa were identified as mitochondrially synthesized constituents of complex I (ND gene products). In the beef heart enzyme the ND-1 product was detected to be among the polypeptides reacting with the inhibitor. 5. Competition experiments employing either NADH or decylbenzoquinone (DB), together with the pethidine analogue, showed that both enzyme substrates interfere specifically with the inhibitor binding to complex I.

Affinity Labels↗
PubMed1990

Examination by fluorescence and EPR spectroscopy of the state of mitochondrial and lysosomal membranes upon freeze-thawing.

The results of spectroscopic examination of mitochondria and lysosomes indicate that freeze-thawing leads to alterations of different character and extent in membrane structural organization which manifest as changes in the molecular packing of the organelle membrane lipid bilayer, lateral separation of lipids into individual domains, and impairment of membrane permeability. Supercooling of organelle suspensions without crystallization of external water has been found not to affect membrane barrier function markedly; however, such a decrease in the temperature results in a slight loosening of the membrane with an increase in the volume of subcellular structures. The crystallization of external water causes dehydration of organelles, which favors a decrease in their volume, increasing the viscosity of the liquid phase inside subcellular structures and packing the lipid bilayer. Changes in the permeability of mitochondrial and lysosomal membranes manifest during thawing after the formation of an external liquid phase and might be due to the sharp rehydration of these membranes through latent membrane defects formed upon freezing.

Animals↗
PubMed1990

Sequence and developmental expression of the mRNA encoding the seleno-protein of the sperm mitochondrial capsule in the mouse.

We have characterized cDNA clones encoding the selenium-containing polypeptide of the keratinous mitochondrial capsule in mouse sperm. The longest open reading frame encodes a polypeptide 143 amino acids long which contains 21% cysteine and 27% proline and closely resembles the size and amino acid composition of bull mitochondrial capsule seleno-protein (V. Pallini, B. Baccetti, and A. G. Burrini, 1979, in "The Spermatozoon," D. W. Fawcett and J. M. Bedford, Eds., pp. 141-151, Urban & Schwartzenberg, Baltimore/Munich). The reading frame encoding the mitochondrial capsule seleno-protein ends with an amber stop codon suggesting that selenium is not incorporated cotranslationally into the protein by an opal suppressor selenocysteyl-tRNA as has been found for several eukaryotic and bacterial proteins. Northern blots using RNA extracted from purified spermatogenic cells and staged prepuberal mice suggest that the mitochondrial capsule seleno-protein mRNA is first transcribed in late meiotic cells and that the levels of the mRNA increase after meiosis in early haploid cells. Southern blots demonstrate that there is one copy of the gene in the mouse genome. The identification of this cDNA clone, in combination with previous work (K. C. Kleene, 1989, Development 106, 367-373) demonstrates that the mRNA for the mitochondrial capsule seleno-protein is translationally repressed with long homogenous poly(A) tracts in round spermatids and translationally active with shortened heterogenous poly(A) tracts in elongating spermatids.

Amino Acid Sequence↗