Modes of coenzyme Q function in electron transfer

PROTOPLASMA ◽  
1995 ◽  
Vol 184 (1-4) ◽  
pp. 50-62 ◽  
Author(s):  
G. Lenaz ◽  
Carla Bovina ◽  
Cinzia Castelluccio ◽  
Marika Cavazzoni ◽  
E. Estornell ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Coenzyme Q ◽  
Q Function

scholarly journals 6-Hydroxypseudooxynicotine Dehydrogenase Delivers Electrons to Electron Transfer Flavoprotein during Nicotine Degradation by Agrobacterium tumefaciens S33

2019 ◽  
Vol 85 (11) ◽  
Author(s):  
Rongshui Wang ◽  
Jihong Yi ◽  
Jinmeng Shang ◽  
Wenjun Yu ◽  
Zhifeng Li ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Agrobacterium Tumefaciens ◽  
Electron Transport ◽  
Electron Acceptor ◽  
Aromatic Compounds ◽  
Coenzyme Q ◽  
Content Type ◽  
Electron Transfer Flavoprotein ◽  
Nicotine Degradation

ABSTRACT Agrobacterium tumefaciens S33 degrades nicotine via a novel hybrid of the pyridine and the pyrrolidine pathways. The hybrid pathway consists of at least six steps involved in oxidoreductive reactions before the N-heterocycle can be broken down. Collectively, the six steps allow electron transfer from nicotine and its intermediates to the final acceptor O2 via the electron transport chain (ETC). 6-Hydroxypseudooxynicotine oxidase, renamed 6-hydroxypseudooxynicotine dehydrogenase in this study, has been characterized as catalyzing the fourth step using the artificial electron acceptor 2,6-dichlorophenolindophenol. Here, we used biochemical, genetic, and liquid chromatography-mass spectrometry (LC-MS) analyses to determine that 6-hydroxypseudooxynicotine dehydrogenase utilizes the electron transfer flavoprotein (EtfAB) as the physiological electron acceptor to catalyze the dehydrogenation of pseudooxynicotine, an analogue of the true substrate 6-hydroxypseudooxynicotine, in vivo, into 3-succinoyl-semialdehyde-pyridine. NAD(P)+, O2, and ferredoxin could not function as electron acceptors. The oxygen atom in the aldehyde group of the product 3-succinoyl-semialdehyde-pyridine was verified to be derived from H2O. Disruption of the etfAB genes in the nicotine-degrading gene cluster decreased the growth rate of A. tumefaciens S33 on nicotine but not on 6-hydroxy-3-succinoylpyridine, an intermediate downstream of the hybrid pathway, indicating the requirement of EtfAB for efficient nicotine degradation. The electrons were found to be further transferred from the reduced EtfAB to coenzyme Q by the catalysis of electron transfer flavoprotein:ubiquinone oxidoreductase. These results aid in an in-depth understanding of the electron transfer process and energy metabolism involved in the nicotine oxidation and provide novel insights into nicotine catabolism in bacteria. IMPORTANCE Nicotine has been studied as a model for toxic N-heterocyclic aromatic compounds. Microorganisms can catabolize nicotine via various pathways and conserve energy from its oxidation. Although several oxidoreductases have been characterized to participate in nicotine degradation, the electron transfer involved in these processes is poorly understood. In this study, we found that 6-hydroxypseudooxynicotine dehydrogenase, a key enzyme in the hybrid pyridine and pyrrolidine pathway for nicotine degradation in Agrobacterium tumefaciens S33, utilizes EtfAB as a physiological electron acceptor. Catalyzed by the membrane-associated electron transfer flavoprotein:ubiquinone oxidoreductase, the electrons are transferred from the reduced EtfAB to coenzyme Q, which then could enter into the classic ETC. Thus, the route for electron transport from the substrate to O2 could be constructed, by which ATP can be further sythesized via chemiosmosis to support the baterial growth. These findings provide new knowledge regarding the catabolism of N-heterocyclic aromatic compounds in microorganisms.

The site of inhibition of mitochondrial electron transfer by coenzyme Q analogues

1978 ◽  
Vol 191 (1) ◽  
pp. 306-315 ◽  
Author(s):  
Henry Roberts ◽  
Wan Mee Choo ◽  
Stuart C. Smith ◽  
Sangkot Marzuki ◽  
Anthony W. Linnane ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Coenzyme Q

scholarly journals Effects of vitamin A deficiency on mitochondrial function in rat liver and heart

2000 ◽  
Vol 84 (6) ◽  
pp. 927-934 ◽  
Author(s):  
Ernesto Estornell ◽  
José R. Tormo ◽  
Pilar Marín ◽  
Jaime Renau-Piqueras ◽  
Joaquín Timoneda ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Vitamin A ◽  
Complex I ◽  
Vitamin A Deficiency ◽  
Coenzyme Q ◽  
Control Diet ◽  
Male Rats ◽  
Heart Mitochondria ◽  
Complex Ii ◽  
Oxidation Rates

The aim of this study was to investigate comparative effects of vitamin A deficiency on respiratory activity and structural integrity in liver and heart mitochondria. Male rats were fed a liquid control diet (control rats) or a liquid vitamin A-deficient diet (vitamin A-deficient rats) for 50 days. One group of vitamin-A deficient rats was refed a control diet for 15 days (vitamin A-recovered rats). To assess the respiratory function of mitochondria the contents of coenzyme Q (ubiquinone, CoQ), cytochrome c and the activities of the whole electron transport chain and of each of its respiratory complexes were evaluated. Chronic vitamin A deficiency promoted a significant increase in the endogenous coenzyme Q content in liver and heart mitochondria when compared with control values. Vitamin A deficiency induced a decrease in the activity of complex I (NADH–CoQ reductase) and complex II (succinate–CoQ reductase) and in the levels of complex I and cytochrome c in heart mitochondria. However, NADH and succinate oxidation rates were maintained at the control levels due to an increase in the CoQ content in accordance with the kinetic behaviour of CoQ as an homogeneous pool. On the contrary, the high CoQ content did not affect the electron-transfer rate in liver mitochondria, whose integrity was preserved from the deleterious effects of the vitamin A deficiency. Ultrastuctural assessment of liver and heart showed that vitamin A deficiency did not induce appreciable alterations in the morphology of their mitochondria. After refeeding the control diet, serum retinol, liver and heart CoQ content and the activity of complex I and complex II in heart mitochondria returned to normality. However, the activities of both whole electron transfer chain and complex I in liver were increased over the control values. The interrelationships between physiological antioxidants in biological membranes and the beneficial effects of their administration in mitochondrial diseases are discussed.

An analysis of the role of coenzyme Q in free radical generation and as an antioxidant

1992 ◽  
Vol 70 (6) ◽  
pp. 390-403 ◽  
Author(s):  
Robert E. Beyer
Keyword(s):  
Electron Transfer ◽  
Superoxide Dismutase ◽  
Free Radical ◽  
Human Subjects ◽  
Coenzyme Q ◽  
Quinone Reductase ◽  
Vital Role ◽  
Free Radical Damage ◽  
Dt Diaphorase

The vital role of coenzyme Q in mitochondrial electron transfer and its regulation, and in energy conservation, is well established. However, the role of coenzyme Q in free oxyradical formation and as an antioxidant remains controversial. Demonstration of the existence of the semiquinone form of coenzyme Q during electron transport, coupled with recent evidence that hydrogen peroxide (but not molecular oxygen) may act as an oxidant of the semiquinone, suggests that the highly reactive OH∙ radical may be formed from the semiquinone. On the other hand, data exist implicating the Fe–S species as the source of electron transfer chain, free radical production. Additional data exist suggesting instead that the unpaired electron of the coenzyme Q semiquinone most likely dismutates superoxide radicals. These concepts and those arising from observations at several levels of organization including subcellular systems, intact animals, and human subjects in the clinical setting, supporting the concept of reduced coenzyme Q as an antioxidant, will be presented. The results of recent studies on the interaction between the two-electron quinone reductase – DT diaphorase and coenzyme Q10 will be presented. The possibility that superoxide dismutase may interact with reduced coenzyme Q, in conjunction with DT diaphorase inhibiting its autoxidation, will be described. The regulation of cellular coenzyme Q concentrations during oxidative stress accompanying aerobic exercise, resulting in increased protection from free radical damage, will also be presented.Key words: coenzyme Q, ubiquinone, free radicals, lipid peroxidation, antioxidant, DT diaphorase, superoxide dismutase, review.

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