Amount Of Ubiquinone Research Articles

Molecular Mechanism of Maternal Rescue in the clk-1 Mutants of Caenorhabditis elegans

The clk-1 mutants of Caenorhabditis elegans display an average slowing down of physiological rates, including those of development, various behaviors, and aging. clk-1 encodes a hydroxylase involved in the biosynthesis of the redox-active lipid ubiquinone (co-enzyme Q), and in clk-1 mutants, ubiquinone is replaced by its biosynthetic precursor demethoxyubiquinone. Surprisingly, homozygous clk-1 mutants display a wild-type phenotype when issued from a heterozygous mother. Here, we show that this maternal effect is the result of the persistence of small amounts of maternally derived CLK-1 protein and that maternal CLK-1 is sufficient for the synthesis of considerable amounts of ubiquinone during development. However, gradual depletion of CLK-1 and ubiquinone, and expression of the mutant phenotype, can be produced experimentally by developmental arrest. We also show that the very long lifespan observed in daf-2 clk-1 double mutants is not abolished by the maternal effect. This suggests that, like developmental arrest, the increased lifespan conferred by daf-2 allows for depletion of maternal CLK-1, resulting in the expression of the synergism between clk-1 and daf-2. Thus, increased adult longevity can be uncoupled from the early mutant phenotypes, indicating that it is possible to obtain an increased adult lifespan from the late inactivation of processes required for normal development and reproduction.

Clocked Out: Mice missing clk-1 die young (Mitochondrial respiration)

Ubiquinone plays a key role in the production of useable cellular energy, but the lipid can also cause trouble: It helps manufacture reactive oxygen species (ROS), which likely contribute to aging (see "The Two Faces of Oxygen" ). Previously, scientists identified a nematode gene, clk-1 , that generates ubiquinone and limits life-span. New work suggests that mice lacking the corresponding gene display similar abnormalities as do worms: For example, they make unusually small amounts of ubiquinone and consume less oxygen than normal, although an effect on life-span has yet to be observed. The work opens up new avenues for studying the role of ubiquinone in mammals and might lead to insights into how ROS production influences aging. Mutations in clk-1 lengthen life-span in Caenorhabditis elegans and also slow embryonic development. The gene encodes an enzyme that enacts a crucial step in the production of chemical energy: It transforms demethoxyubiquinone (DMQ) into ubiquinone (also known as coenzyme Q). Ubiquinone transfers electrons within the mitochondrial respiratory chain, a series of protein stations that convert food energy into adenosine triphosphate (ATP). The exact mechanism by which clk-1 affects life-span is unclear: A dearth of ubiquinone in worms might slow the process--commonly called respiration--enough to reduce the amount of ROS, but that hypothesis has yet to be confirmed. In addition, ubiquinone assists in numerous chemical reactions unrelated to respiration, any of which could affect longevity: For instance, it helps create sulfur bridges within proteins and prevents oxidative damage to cell membranes. To further investigate how clk-1 affects respiration and whether it extends life-span in mammals, two independent research teams created clk-1 -deficient mice. Animals that bear only one copy of the gene function normally, but mice that lack both copies die after about 10 days of embryonic development. Embryos with no clk-1 don't produce detectable amounts of ubiquinone and instead carry unusually high concentrations of DMQ. Similar results were previously observed in C. elegans : clk-1 mutant worms survive embryonic development only when fed ubiquinone; they also accumulate DMQ. But the mechanism by which a lack of clk-1 fouls up embryos is unclear. If respiration ground to a halt in the absence of ubiquinone, cells wouldn't generate enough ATP to support normal development. Electron microscope analysis of mouse embryos missing clk-1 is consistent with that idea: Nakai and colleagues observed misshapen brain cells with enlarged mitochondria that resemble those carried by animals with known defects in the respiratory chain. However, the respiratory chain might not be responsible for the developmental problems in clk-1 mice. Levavasseur and colleagues cultured mouse embryonic stem cells in which clk-1 had been deleted and assessed the function of respiratory enzymes that need ubiquinone to work efficiently. Succinate cytochrome c reductase and NADH-cytochrome c reductase productivity dropped 85% and 35%, respectively, compared to that in normal cells. The cells' oxygen consumption dove 35%. These results suggest that a lack of ubiquinone reduces flow through the respiratory chain but doesn't completely shut it off; the researchers speculate that DMQ might partially substitute for ubiquinone--an idea that is bolstered by the same researchers' other studies in worm mitochondria. Perhaps ubiquinone influences development through one of its functions outside the respiratory chain, they propose. The developmental arrest and large amounts of DMQ in mice without clk-1 indicate that clk-1 exerts some of the same effects in mammals as it does in worms. Whether clk-1 affects longevity in mice remains unclear: The answer might be revealed in future experiments in which researchers knock the gene out of commission only after embryonic development is completed. The new mutant mice offer an additional tool with which to tease apart the functions of ubiquinone and learn how they affect aging. --R. John Davenport; suggested by Chang-Su Lim D. Nakai et al ., Mouse homologue of coq7/clk-1, longevity gene in Caenorhabditis elegans , is essential for coenzyme Q synthesis, maintenance of mitochondrial integrity, and neurogenesis. Biochem. Biophys. Res. Commun. 289 , 463-471 (2001). [Abstract] [Full Text] F. Levavasseur, H. Miyadera, J. Sirois, M. L. Tremblay, K. Kita, E. Shoubridge, S. Hekimi, Ubiquinone is necessary for mouse embryonic development but is not essential for mitochondrial respiration. J. Biol. Chem. 276 , 46160-46164 (2001). [Abstract] [Full Text]

Influence of peroxisome proliferator-activated receptor α on ubiquinone biosynthesis

The control of ubiquinone biosynthesis by peroxisome proliferators was investigated using peroxisome proliferator activated receptor α (PPARα)-null mice. Administration of 2-(diethylhexyl)phthalate to control mice resulted in elevated ubiquinone levels in the liver, while dolichol, dolichyl-P and cholesterol concentrations remained unchanged. In PPARα-null mice, the level of these lipids were similar to control levels and administration of the peroxisome proliferator did not increase the levels of ubiquinone. The increase in ubiquinone levels was the result of increased synthesis. Induction was most pronounced in liver, kidney and heart, which have relatively high levels of PPARα. When the tissue concentration of hydrogen peroxide was elevated by inhibition of catalase activity with aminotriazole, the amount of ubiquinone was not increased, suggesting that the induction of ubiquinone synthesis occured through a direct mechanism. The activities of branch-point enzymes FPP-synthase, squalene synthase, cis-prenyltransferase, trans-prenyltransferase and NPHB-transferase were substantially increased in control but not in PPARα-null mice after treatment with peroxisome proliferators. These data suggest that the induction of ubiquinone biosynthesis after administration of peroxisome proliferators is dependent on the PPARα through regulation of some of the mevalonate pathway enzymes.

Yeast Clk-1 Homologue (Coq7/Cat5) Is a Mitochondrial Protein in Coenzyme Q Synthesis

Mutations in the clk-1 gene result in slower development and increased life span in Caenorhabditis elegans. The Saccharomyces cerevisiae homologue COQ7/CAT5 is essential for several metabolic pathways including ubiquinone biosynthesis, respiration, and gluconeogenic gene activation. We show here that Coq7p/Cat5p is a mitochondrial inner membrane protein directly involved in ubiquinone biosynthesis, and that the defect in gluconeogenic gene activation in coq7/cat5 null mutants is a general consequence of a defect in respiration. These results obtained in the yeast model suggest that the effects on development and life span in C. elegans clk-1 mutants may relate to changes in the amount of ubiquinone, an essential electron transport component and a lipid soluble antioxidant.

Age-dependent modifications in the metabolism of mevalonate pathway lipids in rat brain

The levels and rates of biosynthesis of mevalonate pathway lipids in rat brain were investigated during development and aging. Between birth and 18 months of age there are only moderate decreases in the phospholipid and cholesterol contents but an increase in the levels of dolichyl-P and, particularly of dolichol. The amount of ubiquinone is unchanged. The rate of incorporation of [3H]leucine into protein decreases by 10% during the first year, while the incorporation of [3H]glycerol into phospholipids decreases by 20%. The high rates of [3H]mevalonate incorporation into cholesterol and dolichol after birth decreases rapidly. In contrast, the rate of incorporation into ubiquinone is constant. Squalene synthase activity decreases rapidly in the early postnatal period and at 18 months of age this activity is 10-fold lower than immediately after birth. cis-Prenyltransferase activity is also high during the first postnatal month and reaches a constant level at 4 months of age. Significantly, nonaprenyl 4-hydroxybenzoate transferase activity is high during the entire period investigated. The rate of lipid peroxidation does not change during aging. These results demonstrate that brain cholesterol and dolichol exhibit a low rate of turnover during aging, whereas ubiquinone is synthesized at a high rate and exhibits rapid turnover throughout the entire lifespan.

Effects of sulphate-limited growth in continuous culture on the electron-transport chain and energy conservation in Escherichia coli K12

Growth of Escherichia coli K12 in a chemostat was limited by sulphate concentrations lower than 300 muM. The synthesis of extracellular polysaccharide and a change in morphology accompanied sulphate-limited growth. Growth yields with respect to the amount of glycerol or oxygen consumed were sixfold and twofold lower respectively under these conditions than when growth was limited by glycerol. Sulphate-limited cells lacked the proton-translocating oxidoreduction segment of the electron-transport chain between NADH and the cytochromes, and particles prepared from these cells lacked the energy-dependent reduction of NAD+ by succinate, DL-alpha-glycerophosphate or D-lactate, suggesting the loss of site-I phosphorylation. Glycerol-limited cells contained cytochrome b556, b562 and o, ubiquinone and low concentrations of menaquinone. Sulphate limitation resulted in the additional synthesis of cytochromes d, a1, b558 and c550; the amount of ubiquinone was decreased and menaquinone was barely detectable. Non-haem iron and acid-labile sulphide concentrations were twofold lower in electron-transport particles prepared from sulphate-limited cells. Recovery of site-I phosphorylation could not be demonstrated after incubating sulphate-limited cells with or without glycerol, in either the absence or presence of added sulphate. The loss of site-I phosphorylation in sulphate-limited cells is discussed with reference to the accompanying alterations in cytochrome composition of such cells. Schemes are proposed for the functional organization of the respiratory chains of E. coli grown under conditions of glycerol or sulphate limitation.

Characterization of ubiquinone from vegetative amoebae and mature sorocarps of the cellular slime mold, Dictyostelium Discoideum

1. 1. Ubiquinone, or coenzyme Q, has been isolated from neutral lipid fractions of all developmental stages of the cellular slime mold, Dictyostelium discoideum. 2. 2. The ratio of Q-8 to Q-9 forms was about 2 : 1 in both vegetative and mature sorocarp cells. 3. 3. The amount of ubiquinone in the mature sorocarp is 2.3 mg/g dry weight or 1.5 per cent of the total lipid, a content which is among the highest reported in the literature for any organism.

Regulation of the synthesis of mitochondrial enzymes and cytochromes. Distinction between catabolite repression and anaerobiosis in Saccharomyces cerevisiae.

The possibility that decreased mitochondrial function in anaerobic cultures of Saccharomyces cerevisiae is due to catabolite repression rather than anaerobiosis has been examined using a glucose-limited chemostat. Respiration, cytochromes, ubiquinone and a number of soluble and bound mitochondrial enzymes were measured in cells and cell-free homogenates. Derepression by growth in the chemostat under anaerobic conditions resulted in only small increases in the activity of bound enzymes, and in the amount of ubiquinone and respiration, compared with cells grown batch-wise (repressed). The extent of these increases was much smaller than that seen when cells were grown under aerobic conditions whether repressed or derepressed.