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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interaction between succinate-ubiquinone and ubiquinol-cytochrome c reductases in the purified, dispersed state and in embedded phospholipid vesicles was studied by differential scanning calorimetry and by electron paramagnetic resonance (EPR). When the purified, detergent-dispersed succinate-ubiquinone reductase, ubiquinol-cytochrome c reductase, and cytochrome c oxidase undergo thermodenaturation, they show an endothermic transition. However, when these isolated electron-transfer complexes are embedded in phospholipid vesicles, they undergo exothermodenaturation. The energy released could result from the collapse of the strained interaction between unsaturated fatty acyl groups of phospholipids and an exposed area of the complex formed by removal of interacting proteins. The exothermic enthalpy change of thermodenaturation of a protein-phospholipid vesicle containing both succinate-ubiquinone and ubiquinol-cytochrome c reductases was smaller than that of a mixture of protein-phospholipid vesicles formed from the individual electron-transfer complexes. This suggests specific interaction between succinate-ubiquinone reductase and ubiquinol-cytochrome c reductase in the membrane. This idea is supported by saturation transfer EPR studies showing that the rotational correlation time of spin-labeled ubiquinol-cytochrome c reductase is increased when mixed with succinate-ubiquinone reductase prior to embedding in phospholipid vesicles. These results indicate that succinate-ubiquinone reductase and ubiquinol-cytochrome c reductase are indeed present in the membrane as a supermacromolecular complex. No such supermacromolecular complex is detected between NADH-ubiquinone and ubiquinol-cytochrome c reductases or between succinate-ubiquinone and NADH-uniquinone reductases.
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PMID:Spin-label electron paramagnetic resonance and differential scanning calorimetry studies of the interaction between mitochondrial succinate-ubiquinone and ubiquinol-cytochrome c reductases. 302 58

Rat and pigeon heart mitochondria supplemented with antimycin produce 0.3-1.0nmol of H(2)O(2)/min per mg of protein. These rates are stimulated up to 13-fold by addition of protophores (carbonyl cyanide p-trifluoromethoxyphenylhydrazone, carbonyl cyanide m-chloromethoxyphenylhydrazone and pentachlorophenol). Ionophores, such as valinomycin and gramicidin, and Ca(2+) also markedly stimulated H(2)O(2) production by rat heart mitochondria. The enhancement of H(2)O(2) generation in antimycin-supplemented mitochondria and the increased O(2) uptake of the State 4-to-State 3 transition showed similar protophore, ionophore and Ca(2+) concentration dependencies. Thenoyltrifluoroacetone and N-bromosuccinimide, which inhibit succinate-ubiquinone reductase activity, also decreased mitochondrial H(2)O(2) production. Addition of cyanide to antimycin-supplemented beef heart submitochondrial particles inhibited the generation of O(2) (-), the precursor of mitochondrial H(2)O(2). This effect was parallel to the increase in cytochrome c reduction and it is interpreted as indicating the necessity of cytochrome c(1) (3+) to oxidize ubiquinol to ubisemiquinone, whose autoxidation yields O(2) (-). The effect of protophores, ionophores and Ca(2+) is analysed in relation to the propositions of a cyclic mechanism for the interaction of ubiquinone with succinate dehydrogenase and cytochromes b and c(1) [Wikstrom & Berden (1972) Biochim. Biophys. Acta283, 403-420; Mitchell (1976) J. Theor. Biol.62, 337-367]. A collapse in membrane potential, increasing the rate of ubisemiquinone formation and O(2) (-) production, is proposed as the molecular mechanism for the enhancement of H(2)O(2) formation rates observed on addition of protophores, ionophores and Ca(2+).
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PMID:Enhancement of hydrogen peroxide formation by protophores and ionophores in antimycin-supplemented mitochondria. 740 88

We used a culture-independent approach, namely, thermal gradient gel electrophoresis (TGGE) analysis of ribosomal sequences amplified directly from community DNA, to determine changes in the structure of the microbial community following phenol shocks in the highly complex activated sludge ecosystem. Parallel experimental model sewage plants were given shock loads of chlorinated and methylated phenols and simultaneously were inoculated (i) with a genetically engineered microorganism (GEM) able to degrade the added substituted phenols or (ii) with the nonengineered parental strain. The sludge community DNA was extracted, and 16S rDNA was amplified and analyzed by TGGE. To allow quantitative analysis of TGGE banding patterns, they were normalized to an external standard. The samples were then compared with each other for similarity by using the coefficient of Dice. The Shannon index of diversity, H, was calculated for each sludge sample, which made it possible to determine changes in community diversity. We observed a breakdown in community structure following shock loads of phenols by a decrease in the Shannon index of diversity from 1.13 to 0.22 in the noninoculated system. Inoculation with the GEM (Pseudomonas sp. strain B13 SN45RE) effectively protected the microbial community, as indicated by the maintenance of a high diversity throughout the shock load experiment (H decreased from 1.03 to only 0.82). Inoculation with the nonengineered parental strain, Pseudomonas sp. strain B13, did not protect the microbial community from being severely disturbed; H decreased from 1.22 to 0.46 for a 3-chlorophenol-4-methylphenol shock and from 1.03 to 0.70 for a 4-chlorophenol-4-methylphenol shock. The catabolic trait present in the GEM allowed for bioprotection of the activated sludge community from breakdown caused by toxic shock loading. In-depth TGGE analysis with similarity and diversity algorithms proved to be a very sensitive tool to monitor changes in the structure of the activated sludge microbial community, ranging from subtle shifts during adaptation to laboratory conditions to complete collapse following pollutant shocks.
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PMID:Thermal gradient gel electrophoresis analysis of bioprotection from pollutant shocks in the activated sludge microbial community. 987 66

The N-terminal sequence of apolipoprotein B (apoB) is critical in triacylglycerol-rich lipoprotein assembly. The first 17% of apoB (B17) is thought to consist of three domains: B5.9, a beta-barrel, B6.4-13, a series of 17 alpha-helices, and B13-17, a putative beta-sheet. B5.9 does not bind to lipid, while B6.4-13 and B13-17 contain hydrophobic interfaces that can interact with lipids. To understand how B6.4-13 and B13-17 might interact with triacylglycerol during lipoprotein assembly, the interfacial properties of both peptides were studied at the triolein/water interface. Both B6.4-13 and B13-17 are surface active. Once bound, the peptides can be neither exchanged nor pushed off the interface. Some residues of the peptides can be ejected from the interface upon compression but readsorb on expansion. B13-17 binds to the interface more strongly. The maximum pressure the peptide can withstand without being partially ejected (Pi(max)) is 19.2 mN/m for B13-17 compared to 16.7 mN/m for B6.4-13. B13-17 is purely elastic at the interface, while B6.4-13 forms a viscous-elastic film. When they are spread at an air/water interface, the limiting area and the collapse pressures are 16.6 A(2)/amino acid and 31 mN/m for B6.4-13 and 17.8 A(2)/amino acid and 35 mN/m for B13-17, respectively. The alpha-helical B6.4-13 contains some hydrophobic helices that stay bound and prevent the peptide from leaving the surface. The beta-sheets of B13-17 bind irreversibly to the surface. We suggest that during lipoprotein assembly, the N-terminal apoB starts recruiting lipid as early as B6.4, but additional sequences are essential for formation of a lipid pocket that can stabilize lipoprotein emulsion particles for secretion.
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PMID:Interfacial properties of apolipoprotein B292-593 (B6.4-13) and B611-782 (B13-17). Insights into the structure of the lipovitellin homology region in apolipoprotein B. 2035 82