Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.99.3 (diaphorase)
 5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have investigated the role of the Coenzyme Q pool in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria. Antimycin A and myxothiazol inhibit glycerol-3-phosphate cytochrome c oxidoreductase in a sigmoidal fashion, indicating that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III. The inhibition of ubiquinol cytochrome c reductase is linear at low concentrations of both inhibitors, indicating that sigmoidicity of antimycin A and myxothiazol inhibition is not a direct property of antimycin A and myxothiazol binding. Glycerol-3-phosphate cytochrome c oxidoreductase is strongly stimulated by added CoQ3, indicating that endogenous CoQ is not saturating. Application of the pool equation for nonsaturating ubiquinone allows calculation of the Km for endogenous CoQ of glycerol-3-phosphate dehydrogenase of 3.14 mM. The results of this investigations reveal that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III in brown adipose tissue mitochondria; moreover, its concentration is far below saturation for maximal electron transfer activity in comparison with other branches of the respiratory chain connected with the CoQ pool. HPLC analysis revealed a lower amount of CoQ in brown adipose mitochondria (0.752 nmol/mg protein) in comparison with mitochondria from other tissues and the presence of both CoQ9 and CoQ10.
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PMID:Coenzyme Q-pool function in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria. 132 18

Trypanosoma cruzi epimastigotes permeabilized with digitonin (65 micrograms (mg protein)-1) to measure mitochondrial respiration were exposed to different substrates. Although none of the NADH-dependent substrates stimulated respiration, succinate supported not only oxygen consumption but also oxidative phosphorylation (respiratory control ratio of 1.9 +/- 0.3) indicating that the mitochondria were coupled. The rate of NADH-dependent oxygen consumption by membrane fractions (9.4 +/- 0.7 nmol min-1 (mg protein)-1) was reduced by 50% upon addition of catalase indicating that the electrons from NADH oxidation reduced oxygen to H2O2. NADH-dependent H2O2 production (16 +/- 1 nmol min-1 (mg protein)-1) was confirmed using cytochrome c peroxidase. This activity was inhibited by fumarate by 70%, suggesting a competition between fumarate and oxygen for the electrons from NADH, probably at the fumarate reductase level. The respiratory chain inhibitor antimycin blocked both respiration by intact cells and succinate-dependent cytochrome c by isolated membranes. No inhibition by antimycin was observed when NADH replaced succinate as an electron donor, indicating that the electrons from NADH oxidation reduced cytochrome c through a different route. Malonate blocked not only succinate-cytochrome c reductase and fumarate reductase, but also intact cell motility. These results suggest that succinate has a central role in the intermediate metabolism of i. cruzi, as it may be used for respiration or excreted to the extracellular space under anaerobic conditions. In addition, 2 potential sources of H2O2 were tentatively identified as: (a) the enzyme fumarate reductase; and (b) a succinate-dependent site, which may be the semiquinone form of Coenzyme Q9, as in mammalian mitochondria.
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PMID:Succinate-dependent metabolism in Trypanosoma cruzi epimastigotes. 151 31

We have undertaken a study of the role of coenzyme Q (CoQ) in glycerol-3-phosphate oxidation in mitochondrial membranes from hamster brown adipose tissue, using either quinone homologs, as CoQ1 and CoQ2, or the analogs duroquinone and decylubiquinone as artificial electron acceptors. We have found that the most suitable electron acceptor for glycerol-3-phosphate:CoQ reductase activity in situ in the mitochondrial membrane is the homolog CoQ1 yielding the highest rate of enzyme activity (225 +/- 41 nmol x min(-1) x mg(-1) protein). With all acceptors tested the quinone reduction rates were completely insensitive to Complex III inhibitors, indicating that all acceptors were easily accessible to the quinone-binding site of the dehydrogenase preferentially with respect to the endogenous CoQ pool, in such a way that Complex III was kept in the oxidized state. We have also experimentally investigated the saturation kinetics of endogenous CoQ (1.35 nmol/mg protein of a mixture of 70% CoQ9 and 30% CoQ10) by stepwise pentane extraction of brown adipose tissue mitochondria and found a K(m) of the integrated activity of glycerol-3-phosphate cytochrome c reductase for endogenous CoQ of 0.22 nmol/mg protein, indicating that glycerol-3-phosphate-supported respiration is over 80% of V(max) with respect to the CoQ pool. A similar K(m) of 0.19 nmol CoQ/mg protein was found in glycerol-3-phosphate cytochrome c reductase in cockroach flight muscle mitochondria.
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PMID:Steady-state kinetics of reduction of coenzyme Q analogs by glycerol-3-phosphate dehydrogenase in brown adipose tissue mitochondria. 924 3