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)

Mitoplasts were prepared from 3-h ischemic livers in an attempt to define the structural alterations in the inner membrane that may account for the functional deficiencies of ischemic mitochondria. Mitoplasts from both control and ischemic livers had similar specific activities of cytochrome oxidase and succinate-cytochrome c reductase. With both preparations, the specific activity of rotenone-insensitive NADH-cytochrome c reductase was 10-fold lower than in the mitochondria from which they were prepared. Ischemic mitoplasts had no respiratory control with ADP, and had a slightly reduced phospholipid to protein ratio and an increased cholesterol to protein ratio. As a result, the cholesterol to phospholipid molar ratio was increased from the control of 0.04 to 0.08. There were also differences in the content of individual phospholipid species. Phosphatidylcholine increased by 15%, while cardiolipin decreased by 60%. There were increases in sphingomyelin and in the lysophospholipids of phosphatidylcholine, ethanolamine, and cardiolipin. Pretreatment with chlorpromazine did not prevent these changes. Linoleic acid was decreased by 35% in ischemic phospholipids, and the content of free fatty acids was increased 4-fold. Electron spin resonance spectroscopy of mitoplasts spin labeled with either 5- or 12-doxyl stearic acid revealed an increased molecular order (decreased fluidity) of ischemic inner mitochondrial membranes consistent with the increased cholesterol to phospholipid ratio. The data indicate activation of a phospholipase A in ischemic mitochondria with the resulting accumulation of products of lipid hydrolysis. This conclusion further emphasizes the close similarity between the structural and functional consequences of ischemia in the intact animal and the effect on isolated mitochondria of the activation of the endogenous phospholipase A. In both cases the major functional alterations are attributable to changes in the permeability of the inner mitochondrial membrane induced by the accumulation of lysophospholipids.
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PMID:Structural alterations of the inner mitochondrial membrane in ischemic liver cell injury. 298 20

We have investigated the steady-state kinetics of ubiquinol-cytochrome c reductase using either ubiquinol-1 or -2 as the donor substrate in mitochondria from Saccharomyces cerevisiae either grown at 36 degrees C or brought from 36 to 10 degrees C at the end of the exponential phase ("thermal shock"). The fatty acid composition of the mitochondrial lipids varied under the two conditions, with an increase of the unsaturation degree in the thermally shocked cells. The fluorescence polarization of the membrane probe diphenylhexatriene incorporated into mitochondria was decreased in a wide temperature range in the thermally shocked cells, in accordance with the fatty acid changes. Also the motion and order parameters of two fatty acid spin labels revealed significant changes in the thermally shocked cells, interpreted as an increase of membrane fluidity brought about by the thermal shock. This increase agrees with the finding that the diffusion coefficient of the ubiquinone homolog Q3 in the membrane, investigated by collisional fluorescence quenching of the membrane probe 12-(9-anthroyl) stearic acid, was consistently increased in the mitochondria from the thermally shocked cells. In spite of the physical changes of the membrane and the increase in the diffusion coefficients of the ubiquinone homolog, the steady-state kinetics of ubiquinol cytochrome c reductase showed no change to be interpreted in terms of a diffusion-limited component. An increase of Vmax of the enzyme in the thermally shocked cells was the result of an increased content of the bc1 complex; both the Km for ubiquinols and the turnover number were almost identical under the two growth conditions, so that the kcat/Km ratio, which approaches the second-order rate constant of substrate interaction with the enzyme active site, was unmodified. This is a demonstration that the ubiquinol cytochrome c reductase activity in S. cerevisiae mitochondria is not diffusion-controlled in the interaction of the donor substrate with the enzymatic protein.
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PMID:Steady-state kinetics of ubiquinol-cytochrome c reductase in Saccharomyces cerevisiae mitochondria: effects of fluidity changes obtained by different growth temperatures. 839 Feb 17