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  • 1
    Electronic Resource
    Electronic Resource
    Investigations on the mechanism of the hypocholesterolemic action of 1-ethoxysilatrane (1990)
    Springer
    Molecular and cellular biochemistry 97 (1990), S. 75-85 
    Details
    ISSN: 1573-4919
    Keywords: 1-ethoxysilatrane ; HMGCoA reductase ; cholesterol biosynthesis ; oxidative phosphorylation ; 7 α-hydroxylase ; bile acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Intraperitoneal administration of the nontoxic silicon compound, 1-ethoxysilatrane, to the rat did not cause proliferation of hepatic mitochondria or of endoplasmic reticulum, nor did it affect mitochondrial oxidative phosphorylation. The activities of cholesterol 7 α-hydroxylase in hepatic microsomes and of cholesterol oxidase in mitochondria respectively were unaffected by silatrane treatment. The rate of release of bile, whose composition remained unchanged, also was not increased in silatrane-treated animals. The results indicated that the compound did not affect the pathway of cholesterol degradation. A progressive decrease in the activity of hepatic microsomal 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase was observed on administration of the compound over a period of three weeks. Consistent with this, cholesterol biosynthesis in liver as measured by incorporation of radioactive precursors, acetate and water but not mevalonate, was significantly decreased in silatrane-treated animals. However, enzyme-linked immunosorbant assay revealed that the concentration of HMGCoA reductase protein was not decreased by the treatment indicating that inactivated enzyme was also present in such microsomes. Addition of silatrane to microsomes in the assay system did not cause inhibition indicating that the inactivation is by an indirect mechanism. It is concluded that the hypocholesterolemic action of the compound rested entirely on the inhibition of cholesterol biosynthesis in vivo by inactivation of the rate-limiting enzyme HMGCoA reductase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231703
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation of a soluble 58kDa-3-hydroxy-3-methylglutaryl CoA reductase from liver microsomes and its inhibition by ethoxysilatrane, a hypocholesterolemic compound (1992)
    Springer
    Molecular and cellular biochemistry 110 (1992), S. 145-153 
    Details
    ISSN: 1573-4919
    Keywords: ethoxysilatrane ; HMGCoA reductase ; mevalonate biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract On repeated thawing at room temperature of frozen preparations of heavy microsomes from rat livers, HMGCoA reductase activity was solubilized due to limited proteolysis. This soluble enzyme was partially purified by fractionation with ammonium sulfate and filtration on Sephacryl S-200 column. The active enzyme was coeluted with a major 92 kDa-protein and was identified as a 58kDa-protein after separation by SDS-PAGE and immunoblotting. Ethoxysilatrane, a hypocholesterolemic compound, which decreased the liver-microsomal activity of HMGCoA reductase on intra-peritonial treatment of animals, showed little effect on the enzyme activity with isolated microsomes or the 50kDa-soluble enzyme when added in the assay. But it was able to inhibit the activity of the soluble 58kDa-enzyme in a concentration-dependent, reversible manner. Cholesterol and an oxycholesterol were without effect whereas chlorophenoxyisobutyrate and ubiquinone showed small inhibition under these conditions. The extra region that links the active site domain (50kDa protein) to the membrane, present in the 58kDa-protein appears to be involved in mediating the inhibition by silatrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02454191
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  • 3
    Electronic Resource
    Electronic Resource
    Ferrous-iron induces lipid peroxidation with little damage to energy transduction in mitochondria (1993)
    Springer
    Molecular and cellular biochemistry 120 (1993), S. 141-149 
    Details
    ISSN: 1573-4919
    Keywords: lipid peroxidation ; ferrous-iron ; mitochondria ; ubiquinone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Addition of ferrous sulfate, but not ferric chloride, in micromolar concentrations to rat liver mitochondria induced high rates of consumption of oxygen. The oxygen consumed was several times in excess of the reducing capacity of ferrous-iron (O: Fe ratios 5–8). This occurred in the absence of NADPH or any exogenous oxidizable substrate. The reaction terminated on oxidation of ferrous ions. Malondialdehyde (MDA), measured as thiobarbituric acid-reacting material, was produced indicating peroxidation of lipids. The ratio of O2: MDA was about 4: 1. Pretreatment of mitochondria with ferrous sulfate decreased the rate of oxidation (state 3) with glutamate (+malate) as the substrate by about 40% but caused little damage to energy tranduction process as represented by ratios of ADP: O and respiratory control, as well as calcium-stimulated oxygen uptake and energy-dependent uptake of [45Ca]-calcium. Addition of succinate or ubiquinone decreased ferrous iron-induced lipid peroxidation in intact mitochondria. In frozen-thawed mitochondria, addition of succinate enhanced lipid peroxidation whereas ubiquinone had little effect. These results suggest that ferrous-iron can cause peroxidation of mitochondrial lipids without affecting the energy transduction systems, and that succinate and ubiquinone can offer protection from damage due to such ferrous-iron released from the stores within the cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00926087
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  • 4
    Electronic Resource
    Electronic Resource
    Microsomal redox systems in brown adipose tissue: high lipid peroxidation, low cholesterol biosynthesis and no detectable cytochrome P-450 (1990)
    Springer
    Molecular and cellular biochemistry 92 (1990), S. 147-157 
    Details
    ISSN: 1573-4919
    Keywords: microsomal redox systems ; brown adipose tissue ; lipid peroxidation ; cholesterol biosynthesis ; cytochrome P-450
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The presence of redox systems in microsomes of brown adipose tissue (BAT) in cold exposed rats was investigated and compared with liver. BAT microsomes showed high activity of lipid peroxidation measured both by the formation of malondialdehyde (MDA) and by oxygen uptake. NADH and NADPH dependent cytochrome c reductase activity were present in both BAT and liver microsomes. Aminopyrine demethylase and aniline hydroxylase activities, the characteristic detoxification enzymes in liver microsomes could not be detected in BAT microsomes. BAT minces showed very poor incorporation of [1-14C]acetate and [2-14C]-mevalonate in unsaponifiable lipid fraction compared to liver. Biosynthesis of cholesterol and ubiquinone, but not fatty acids, and the activity of 3-hydroxy-3-methyl glutaryl CoA reductase appear to be very low in BAT. Examination of difference spectra showed the presence of only cytochrome b 5 in BAT microsomes. In addition to the inability to detect the enzyme activities dependent on cytochrome P-450, a protein with the characteristic spectrum, molecular size in SDS-PAGE and interaction with antibodies in double diffusion test, also could not be detected in BAT microsomes. The high activity of lipid peroxidation in microsomes, being associated with large oxygen uptake and oxidation of NADPH, will also contribute to the energy dissipation as heat in BAT, considered important in thermogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00218132
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  • 5
    Electronic Resource
    Electronic Resource
    Increase in hepatic microsomal lipid peroxidation mediated by α-adrenergic system under cold stress and noradrenaline treatment (1990)
    Springer
    Molecular and cellular biochemistry 94 (1990), S. 61-70 
    Details
    ISSN: 1573-4919
    Keywords: lipid peroxidation ; α-adrenergic receptors ; non-shivering thermogenesis ; noradrenaline ; phenoxybenzamine ; cold and heat exposure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Lipid peroxidation measured both by the formation of malondialdehyde and by oxygen uptake in presence of NADPH, Fe2− and ADP in hepatic microsomes increased on cold exposure and decreased on heat exposure of rats. Malondialdehyde content of isolated microsomes also showed similar changes. Treatment of animals with noradrenaline or a a-adrenergic agonist, phenylephrine, increased lipid peroxidation which was prevented by simultaneous treatment with cycloheximide, a protein synthesis inhibitor. Cold- and noradrenaline-induced increases were not found in animals pretreated with a-adrenergic receptor antagonist, phenoxybenzamine, but not with propranolol, a β-adrenergic blocking agent. The concentration of the microsomal cytochromes P-450 and b 5 remained unaffected under these conditions but the activity of NADPH-cytochrome c reductase showed parallel changes. These observations suggest a role for lipid peroxidation in cellular thermogenesis in liver tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223563
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  • 6
    Electronic Resource
    Electronic Resource
    Brown adipose tissue mitochondria are cytochrome c — subsaturated (1991)
    Springer
    Molecular and cellular biochemistry 105 (1991), S. 119-125 
    Details
    ISSN: 1573-4919
    Keywords: BAT mitochondria ; electron transport ; stimulation ; cytochrome c binding sites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The oxidative activity of mitochondria freshly isolated from brown adipose tissue of rats was stimulated two-fold on the addition of small concentrations of exogenous cytochrome c to the reaction medium. Loss of membrane-bound cytochrome c did not occur during isolation of mitochondria. Estimation of the high-affinity binding sites on the organelle membrane indicated that less than a third of these sites remained saturated with cytochrome c. The pigment is thus shown to be a functionally limiting electron transport component in brown adipose tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227751
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  • 7
    Electronic Resource
    Electronic Resource
    NADH-dependent polyvanadate reduction by microsomes (1987)
    Springer
    Molecular and cellular biochemistry 75 (1987), S. 161-167 
    Details
    ISSN: 1573-4919
    Keywords: microsomes ; polyvanadate reduction ; cytochrome b 5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract NADH-dependent reduction of polyvanadate was observed by using rat liver microsomes as the enzyme source. The reduced vanadate form obtained was blue in color with a broad absorption maximum in the red region around 650 nm. Microsomes and phosphate anions were found to be essential for polyvanadate reduction. The rate and the extent of formation of blue color compound was dependent on the amount of vanadate present. Cytochrome b 5 was found to be involved in this SOD-insensitive reaction. The rate of disappearance of the blue-colored compound was dependent on concentration of NADH and was found to be sensitive to SOD. Catalase and Mn2+. which inhibit oxygen consumption accompanying NADH oxidation, increased both the rate and extent of the blue color compound formed. The results suggest that vanadate acts as an electron acceptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229904
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  • 8
    Electronic Resource
    Electronic Resource
    Vanadate-stimulated NADH oxidation in microsomes (1987)
    Springer
    Molecular and cellular biochemistry 75 (1987), S. 151-159 
    Details
    ISSN: 1573-4919
    Keywords: microsomes ; NADH oxidation ; SOD-sensitive ; O2 uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Addition of vanadate, stimulated oxidation of NADH by rat liver microsomes. The products were NAD+ and H2O2. High rates of this reaction were obtained in the presence of phosphate buffer and at low pH values. The yellow-orange colored polymeric form of vanadate appears to be the active species and both ortho- and meta-vanadate gave poor activities even at mM concentrations. The activity as measured by oxygen uptake was inhibited by cyanide, EDTA, mannitol, histidine, ascorbate, noradrenaline, adriamycin, cytochrome c, Mn2+, superoxide dismutase, horseradish peroxidase and catalase. Mitochondrial outer membranes possess a similar activity of vanadate-stimulated NADH oxidation. But addition of mitochondria and some of its derivative particles abolished the microsomal activity. In the absence of oxygen, disappearance of NADH measured by decrease in absorbance at 340 nm continued at nearly the same rate since vanadate served as an electron acceptor in the microsomal system. Addition of excess catalase or SOD abolished the oxygen uptake while retaining significant rates of NADH disappearance indicating that the two activities are delinked. A mechanism is proposed wherein oxygen receives the first electron from NAD radical generated by oxidation of NADH by phosphovanadate and the consequent reduced species of vanadate (Viv) gives the second electron to superoxide to reduce it H2O2. This is applicable to all membranes whereas microsomes have the additional capability of reducing vanadate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229903
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  • 9
    Electronic Resource
    Electronic Resource
    Influence of cerebral ischemia and post-ischemic reperfusion on mitochondrial oxidative phosphorylation (1990)
    Springer
    Journal of bioenergetics and biomembranes 22 (1990), S. 61-80 
    Details
    ISSN: 1573-6881
    Keywords: Ischemia ; brain mitochondria ; respiration ; calcium transport ; adenine nucleotide translocase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Unilateral ischemia in the right cerebral hemisphere of the rat was induced by ligation of the right common carotid artery coupled with controlled hemorrhage to produce hypotension (25±8 mm/Hg). Where indicated after 30 min of ischemia, the withdrawn blood was reinfused to restore arterial pressure to normal. Mitochondria isolated from the ipsilateral hemisphere after 30 min of ischemia showed significantly lower respiratory rates than the organelles isolated from the contralateral side. Oxidation of NAD+-linked substrates was more sensitive to inhibition in ischemia (30%) than was of ferrocytochromec (12%), succinate oxidation being intermediate. The activities of membrane-bound dehydrogenases (both NADH and succinate-linked) were also significantly lowered. Ischemia did not affect the cytochrome content of mitochondria. Respiratory activity (NAD+-linked) of mitochondria isolated from the ipsilateral hemisphere was twice as sensitive to inhibition by fatty acid as was of preparations from the contralateral side. Mitochondria isolated from cerebral cortex after 90 min of post-ischemic reperfusion showed no significant improvement in the rate of substrate oxidation. Adenine nucleotide translocase activity and energy-dependent Ca2+ uptake, both of which decreased significantly in mitochondria isolated from the ischemic brain, showed little recovery, on reperfusion. These observations suggested the strong possibility that the deleterious effects of ischemia on mitochondrial respiratory function might be mediated by free fatty acids that are known to accumulate in large amounts in ischemic tissues. The pattern of inhibition of ATPase activity was consistent with this view.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00762846
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  • 10
    Electronic Resource
    Electronic Resource
    Oxidations in kidney mitochondria of heat-exposed rats: Regulation by cytochromec (1984)
    Springer
    Journal of bioenergetics and biomembranes 16 (1984), S. 421-431 
    Details
    ISSN: 1573-6881
    Keywords: Regulation of state 3 oxidation by cytochromec ; decrease in H2O2 generation ; α-glycerophosphate dehydrogenase ; cytochromec in mitochondria ; stress heat ; propylthiouracil treatment ; starvation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Exposure of rats to higher environmental temperature (36–37°C) decreased the capacity of their kidney mitochondria to oxidize succinate. The decrease was corrected on the addition of exogenous cytochromec. Kidney mitochondria of heat-exposed animals showed decreased rates of H2O2 generation when α-glycerophosphate, but not succinate, was used as electron donor. These mitochondria also showed decreased activity of α-glycerophosphate dehydrogenase but not of succinate dehydrogenase. The content of cytochromec in kidney mitochondria of heat-exposed animals was low even though the concentration of the pigment in the whole tissue did not decrease. Starvation as well as administration of an antithyroid agent like propylthiouracil simulated some of the effects of heat exposure on kidney mitochondria, but the cytochromec-dependent reversal of inhibition of oxidation was obtained only in heat exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00743236
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