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PubMed1990

Mitochondrial complex I deficiency in Parkinson's disease.

The structure and function of mitochondrial respiratory-chain enzyme proteins were studied postmortem in the substantia nigra of nine patients with Parkinson's disease and nine matched controls. Total protein and mitochondrial mass were similar in the two groups. NADH-ubiquinone reductase (Complex I) and NADH cytochrome c reductase activities were significantly reduced, whereas succinate cytochrome c reductase activity was normal. These results indicated a specific defect of Complex I activity in the substantia nigra of patients with Parkinson's disease. This biochemical defect is the same as that produced in animal models of parkinsonism by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and adds further support to the proposition that Parkinson's disease may be due to an environmental toxin with action(s) similar to those of MPTP.

Electron Transport Complex II↗
PubMed2004

Effects of aerobic training on pyruvate dehydrogenase and pyruvate dehydrogenase kinase in human skeletal muscle.

This study examined the effects of short- and long-term aerobic training on the stable up-regulation of pyruvate dehydrogenase (PDH) and PDH kinase (PDK) in human skeletal muscle. We hypothesized that 8 weeks, but not 1 week, of aerobic training would increase total PDH (PDHt) and PDK activities compared to pretraining, and this would be detectable at the level of gene transcription (mRNA) and/or gene translation (protein). Resting muscle biopsies were taken before and after 1 and 8 weeks of aerobic cycle exercise training. PDHt and PDK activities, and their respective protein and mRNA expression, did not differ after 1 week of aerobic training. PDHt activity increased 31% after 8 weeks and this may be partially due to a 1.3-fold increase in PDH-E(1)alpha protein expression. PDK activity approximately doubled after 8 weeks of aerobic training and this was attributed to a 1.3-fold increase in PDK2 isoform protein expression. Similar to 1 week, no changes were observed at the mRNA level after 8 weeks of training. These findings suggest that aerobically trained human skeletal muscle has an increased maximal capacity to utilize carbohydrates, evident by increased PDHt, but increased metabolic control sensitivity to pyruvate through increased contribution of PDK2 to total PDK activity.

Adaptation, Physiological↗
PubMed1964

COENZYME Q: REVERSAL OF INHIBITION OF SUCCINATE CYTOCHROME C REDUCTASE BY LIPOPHILIC COMPOUNDS.

The activity of a particulate succinate cytochrome c reductase is inhibited by antimycin, 2-heptyl-4-hydroxyquinoline-N-oxide, 2-(9-cyclohexyl-n-nonyl)-3-hydroxy-1,4naphthoquinone and thenoyltrifluoroacetone. The ratio of antimycin A (required for complete inhibition) to the molar content of the cytochrome b of the reductase is approximately 0.5 in contrast to the reported value of 1.0 or higher for succinate oxidase preparations. However, the degreeof inhibition by antimycin is dependent on the exogenous coenzyme Q (ubiquinone) present. Indeed, the inhibition from any of these compounds is competitively reversed by exogenous coenzyme Q in the system.

Antimycin A↗
PubMed1999

Oxidative phosphorylation at the fin de siècle.

Mitochondria produce most of the energy in animal cells by a process called oxidative phosphorylation. Electrons are passed along a series of respiratory enzyme complexes located in the inner mitochondrial membrane, and the energy released by this electron transfer is used to pump protons across the membrane. The resultant electrochemical gradient enables another complex, adenosine 5'-triphosphate (ATP) synthase, to synthesize the energy carrier ATP. Important new mechanistic insights into oxidative phosphorylation have emerged from recent three-dimensional structural analyses of ATP synthase and two of the respiratory enzyme complexes, cytochrome bc1 and cytochrome c oxidase. This work, and new enzymological studies of ATP synthase's unusual catalytic mechanism, are reviewed here.

Adenosine Triphosphate↗
PubMed2001

Structures and proton-pumping strategies of mitochondrial respiratory enzymes.

Enzymes of the mitochondrial respiratory chain serve as proton pumps, using the energy made available from electron transfer reactions to transport protons across the inner mitochondrial membrane and create an electrochemical gradient used for the production of ATP. The ATP synthase enzyme is reversible and can also serve as a proton pump by coupling ATP hydrolysis to proton translocation. Each of the respiratory enzymes uses a different strategy for performing proton pumping. In this work, the strategies are described and the structural bases for the action of these proteins are discussed in light of recent crystal structures of several respiratory enzymes. The mechanisms and efficiency of proton translocation are also analyzed in terms of the thermodynamics of the substrate transformations catalyzed by these enzymes.

Animals↗
PubMed2006

Mitochondrial function and nitric oxide metabolism are modified by enalapril treatment in rat kidney.

The renal and cardiac benefits of renin-angiotensin system (RAS) inhibition in hypertension exceed those attributable to blood pressure reduction, and seem to involve mitochondrial function changes. To investigate whether mitochondrial changes associated with RAS inhibition are related to changes in nitric oxide (NO) metabolism, four groups of male Wistar rats were treated during 2 wk with a RAS inhibitor, enalapril (10 mg x kg(-1) x day(-1); Enal), or a NO synthase (NOS) inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME) (1 mg x kg(-1) x day(-1)), or both (Enal+L-NAME), or were untreated (control). Blood pressure and body weight were lower in Enal than in control. Electron transfer through complexes I to III and cytochrome oxidase activity were significantly lower, and uncoupling protein-2 content was significantly higher in kidney mitochondria isolated from Enal than in those from control. All of these changes were prevented by L-NAME cotreatment and were accompanied by a higher production/bioavailability of kidney NO. L-NAME abolished mitochondrial NOS activity but failed to inhibit extra-mitochondrial kidney NOS, underscoring the relevance of mitochondrial NO in those effects of enalapril that were suppressed by L-NAME cotreatment. In Enal, kidney mitochondria H(2)O(2) production rate and MnSOD activity were significantly lower than in control, and these effects were not prevented by L-NAME cotreatment. These findings may clarify the role of NO in the interactions between RAS and mitochondrial metabolism and can help to unravel the mechanisms involved in renal protection by RAS inhibitors.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Consequences of aging on mitochondrial respiratory chain enzymes in cultured human fibroblasts treated with ascorbate.

The activities of mitochondrial respiratory chain enzymes with and without ascorbate pretreatment were assayed in 10- to 20-week-old cultures of human fibroblasts. Aging was associated with a significant loss of respiratory chain enzyme activities. The presence of ascorbate in the medium reduced the rate of loss of these enzymes. Free radical-mediated injuries may also contribute to aging since the changes seen in respiratory chain enzyme activities are similar to those seen in oxidatively stressed cells. This study demonstrates an age-related decline in mitochondrial respiratory chain activity as well as a protective role for ascorbate in aging.

Ascorbic Acid↗
PubMed2002

Mitochondrial energy metabolism in very premature neonates.

The activity, amount and protein composition of pyruvate dehydrogenase (PDH) and respiratory chain complexes were studied in muscle mitochondria obtained postmortally from 6 neonates with a gestational age of 23-29 weeks. The activities of PDH and respiratory chain complex III and IV and citrate synthase were significantly lower in comparison with control children aged 0.5-2 and 2-20 years. Protein analyses revealed a parallel decrease in the content of PDH, respiratory chain complexes and their subunits in the cases analyzed. The observed immaturity of the mitochondrial energy-providing system suggests that significant development of mitochondrial energy metabolism occurs during the last 3 months of prenatal development. The metabolic disturbances of mitochondrial energy conversion associated with the low functional capacity and content of PDH and respiratory chain complexes may play an important role in the morbidity of very premature neonates.

Adolescent↗
PubMed1991

Studies for the elucidation of the mode of action of the antimycotic hydroxypyridone compound, rilopirox.

Rilopirox is a synthetic, fungicidal antimycotic agent with hydrophobic characteristics. Its chemical name is 6-[4-(4-chlorophenoxy)-phenoxy-methyl]-1-hydroxy-4-methyl-2-pyridone and it has a molecular weight of 357.79. Rilopirox is very soluble in dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) but poorly soluble in water. The amount of antimycotic agent remaining in the solution is dependent on the final concentration of the solvent and the amount of rilopirox used. Complexometric studies show that rilopirox has a high affinity for iron ions [unpubl. data]. Catalase, an iron-containing enzyme, is inhibited by the chelating agent rilopirox. Studies on yeast mitochondria and submitochondrial particles show that rilopirox inhibits the respiratory chain. Complex I (NADH-ubiquinone oxidoreductase) contains iron-sulfur proteins and is the main system which is inhibited.

Antifungal Agents↗