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At least 91 records · Page 5Linked to original sources
PubMed1992

Respiratory chain enzymes in muscle of endurance athletes: effect of L-carnitine.

The effects of L-carnitine on respiratory chain enzymes in muscle of long distance runners were studied in 14 athletes. These subjects received placebo or L-carnitine (2 g orally b.i.d.) during a 4-week period of training. Athletes receiving L-carnitine showed a significant increase (p < 0.01) in the activities of rotenone-sensitive NADH cytochrome c reductase, succinate cytochrome c reductase and cytochrome oxidase. In contrast, succinate dehydrogenase and citrate synthase were unchanged. No significant changes were observed after placebo administration. The levels of both total and free carnitine from athletes receiving placebo were significantly decreased (p < 0.01) after treatment. By contrast, total and free carnitine levels were markedly increased (p < 0.01) after supplementation with L-carnitine. Our results suggest that L-carnitine induces an increase of the respiratory chain enzyme activities in muscle, probably by mechanisms involving mitochondrial DNA.

Analysis of Variance↗
PubMed1996

Determination of the activities of the enzyme complexes of the electron transport chain in human fibroblasts.

In order to improve the determination of the activities of the enzyme complexes of the electron transport chain (ETC) in fibroblasts, we characterized the isolation of mitochondria and measured enzyme activities in mitochondrial preparations from fibroblasts of control subjects and patients with suspected mitochondrial cytopathy. The isolation procedure yielded 54% of the citrate synthase activity in fibroblasts, with a 6-fold enrichment in this mitochondrial marker enzyme. The activities of the complexes of the ETC were linear with time and with the mitochondrial protein concentration used. The coefficients of variation for the enzyme activities determined were in the range of 10% in mitochondria from identical fibroblast cultures and between 30 and 70% in mitochondria from different fibroblast cultures of the same or of different patients. Decreased activities of one or more enzyme complexes (defined as an activity below the 95% confidence limit of control values) were found in 15 of 22 patients investigated. When compared with activities obtained in liver or skeletal muscle obtained at autopsy, the results were identical in three but different in two patients. The studies show that the activities of the enzyme complexes of the ETC can be determined reliably and reproducibly in mitochondria isolated from fibroblasts and that the results obtained are potentially useful for the diagnosis of mitochondrial cytopathies in patients with suggestive symptoms and signs.

Cells, Cultured↗
PubMed1984

Two distinct quinone-modulated modes of antimycin-sensitive cytochrome b reduction in the cytochrome bc1 complex.

Reduction of cytochrome b-560 (analogous to cyt b-562 of mitochondria) via an antimycin-sensitive route has been revealed in chromatophores of the photosynthetic bacterium, Rhodopseudomonas sphaeroides Ga. Indeed, the results suggest that two reductive mechanisms can be operative. One is consistent with the idea that the quinol generated at the reaction center QB site enters the Q pool and, via the Qc site, equilibrates with cytochrome b-560. The other reductive mode circumvents redox equilibrium with the pool; we consider that this could result from a direct encounter of the reaction center with the bc1 complex perhaps involving a direct QB-Qc site interaction. This latter reaction is suppressed by occupancy of the Qc site, not only by antimycin but by ubiquinol and ubiquinone.

Antimycin A↗
PubMed1991

Multiple defects of the mitochondrial respiratory chain in a mitochondrial encephalopathy (MERRF): a clinical, biochemical and molecular study.

We describe a young man with a progressive neurological disorder including myoclonus, mental retardation, muscle weakness and a mitochondrial myopathy (myoclonus epilepsy and ragged red fibres--MERRF). Multiple abnormalities of the mitochondrial respiratory chain in skeletal muscle are shown by direct measurement of the flux through the individual complexes, low-temperature redox spectroscopy and decreased immunodetectable subunits of complexes I and IV by immunoblotting. No abnormality of mitochondrial DNA was found. This is the first report of combined defects of complexes I, III and IV as a cause of this clinical syndrome. However, we propose that the occurrence of multiple respiratory chain defects may be more common than previously recognised and that this particular combination of defects, involving complexes I, III and IV, may be the predominant biochemical abnormality in MERRF.

Adult↗
PubMed1992

Uneven distribution of mitochondrial DNA mutation in MERRF dizygotic twins.

A new family of myoclonic epilepsy with ragged-red fibers (MERRF) was studied at clinical, histological, biochemical and molecular genetic levels. There was a remarkable variation in the age of onset, the clinical presentation and the severity of symptoms. Multiple defects affecting respiratory chain complexes I, III and IV were detected in 2 patients. The point mutation at 8344 of the mitochondrial genome was found in all the maternal lineage with a relatively narrow range of variation in the percentage of mutant mitochondrial genomes. The one exception was represented by a set of dizygotic twins, one clinically affected and showing high proportions of mutant mitochondrial DNAs (mtDNAs) in blood cells, while the other was asymptomatic and showed very small amounts of mutant mt-DNAs in blood and skin. This could suggest an early segregation of the mitochondrial genome during ovogenesis.

Adult↗
PubMed2003

Common evolutionary origin of mitochondrial and rickettsial respiratory chains.

Comprehensive phylogenetic analysis of the subunits of respiratory chain was carried out using a variety of mitochondrial and bacterial sequences including those from all unfinished alpha-proteobacterial genomes known to date. Maximum likelihood, neighbor-joining, and maximum parsimony consensus trees, based on four proton-translocating complexes, placed mitochondria as a sister group to the order Rickettsiales of obligate endosymbiotic bacteria to the exclusion of free-living alpha-proteobacteria. Thus, phylogenetic relationship of most eukaryotic respiratory enzymes conforms to canonical pattern of mitochondrial ancestry, prior established in analyses of ribosomal RNAs, which are encoded by residual mitochondrial genomes. These data suggest that mitochondria may have derived from a reduced intracellular bacterium and that respiration may be the only evolutionary novelty brought into eukaryotes by mitochondrial endosymbiont.

Alphaproteobacteria↗
PubMed2005

Congenital or late-onset myopathy in patients with the T14709C mtDNA mutation.

Three patients with different clinical phenotypes harbored the same point mutation at nucleotide 14709 (T14709C) in the tRNAGlu gene of mitochondrial DNA (mtDNA). The first patient was a 21-month-old child with severe congenital myopathy, respiratory distress and mild mental retardation. Muscle biopsy showed about 12% cytochrome c oxidase (COX)-negative ragged-red fibers (RRFs), and markedly decreased activities of mitochondrial respiratory chain complexes I, III and IV. The other two patients were 51- and 55-year-old siblings with slowly progressive myopathy and diabetes mellitus. Muscle biopsy showed focal COX-negative RRFs and decreased activities of complexes I, III and IV. In all three patients, the T14709C mutation was abundant in muscle but present at lower levels in accessible tissues. Previously described patients with the same mutation also showed congenital or late-onset myopathy. Diabetes is frequently associated with both phenotypes and is a clinical clue to the molecular diagnosis.

Cysteine↗
PubMed2001

Fungal respiration: a fusion of standard and alternative components.

In animals, electron transfer from NADH to molecular oxygen proceeds via large respiratory complexes in a linear respiratory chain. In contrast, most fungi utilise branched respiratory chains. These consist of alternative NADH dehydrogenases, which catalyse rotenone insensitive oxidation of matrix NADH or enable cytoplasmic NADH to be used directly. Many also contain an alternative oxidase that probably accepts electrons directly from ubiquinol. A few fungi lack Complex I. Although the alternative components are non-energy conserving, their organisation within the fungal electron transfer chain ensures that the transfer of electrons from NADH to molecular oxygen is generally coupled to proton translocation through at least one site. The alternative oxidase enables respiration to continue in the presence of inhibitors for ubiquinol:cytochrome c oxidoreductase and cytochrome c oxidase. This may be particularly important for fungal pathogens, since host defence mechanisms often involve nitric oxide, which, whilst being a potent inhibitor of cytochrome c oxidase, has no inhibitory effect on alternative oxidase. Alternative NADH dehydrogenases may avoid the active oxygen production associated with Complex I. The expression and activity regulation of alternative components responds to factors ranging from oxidative stress to the stage of fungal development.

Amino Acid Sequence↗