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D D Tyler

Publications and source records attributed to D D Tyler.

At least 19 recordsLinked to original sources
PubMed1988

The effect of limit feeding on thermogenesis and thermoregulation in genetically obese (ob/ob) mice during cold exposure.

Thermogenesis and thermoregulation in ad-lib-fed and limit-fed lean (+/ob or +/+) and obese (ob/ob) mice during acute cold exposure were studied by measuring oxygen consumption and body temperature. No significant differences in oxygen consumption were found between the lean ad-lib, obese ad-lib- or obese limit-fed groups. The oxygen consumption of the lean-limit-fed group was decreased by 25-30 per cent compared with the other groups. The body temperature of the obese ad-lib-fed group fell at a rate of at least twice that of any other group. The weight, total cytochrome c oxidase activity and protein content of the brown adipose tissue (BAT) of the lean groups was similar, and there appeared to be little difference in cell size or fat content. The BAT of both obese groups showed a several-fold increase in weight, and a 50 per cent increase in total protein, compared with the lean groups. The limit-fed obese group showed a significant increase in cytochrome c oxidase activity compared with all other groups. The BAT cells of both obese groups were much enlarged and contained considerable amounts of fat. These observations indicate that the susceptibility of obese mice to hypothermia is not due to a reduced capacity for thermogenesis, but to a failure to conserve heat. Failure of thermoregulation in obese animals may be due to postural constraints that result in increased heat loss by radiation. The results are discussed in relation to the accredited role of BAT thermogenesis in rodents exposed to the cold.

Adipose Tissue, Brown↗
PubMed1985

Influence of restricted food intake on brown adipose tissue function in genetically obese mice (genotype, ob/ob).

Measurements were made of cytochrome c oxidase activity and the GDP-binding capacity of mitochondria in brown adipose tissue of genetically obese mice and wild-type siblings, to estimate the thermogenic capacity of the tissue. The binding capacity was decreased in ad libitum fed obese animals compared with wild-type animals. Limited feeding of obese animals to restrict their body weight caused a large increase in the binding capacity of the tissue, which was greater than that in wild-type animals fed either ad limitum or on a limited diet. The decreased binding capacity of brown adipose tissue mitochondria in obese mice appears to be a consequence of ad libitum feeding and therefore not a cause of the obesity. Limit feeding of obese animals also corrected their characteristic hypothermia at low ambient temperature. The large increase in the thermogenic capacity of brown adipose tissue in obese animals, induced by limited feeding, may account for the vital improvement of their thermoregulation. However, close similarities were found between obesity hypothermia and hypothermia induced in wild-type animals by restraint. It is suggested that changes in posture caused by obesity, resulting in increased loss of body heat, may be important in the development of obesity hypothermia. Obese animals fed less than wild-type grained more weight than wild-type animals, indicating that the high thermogenic capacity of their brown adipose tissue did not function to regulate their calorie intake.

Adipose Tissue, Brown↗
PubMed1979

Purification and properties of the adenosine triphosphatase released from the liver mitochondrial membrane by chloroform.

1. Soluble ATPase (adenosine triphosphatase) activity is released when rat liver submitochondrial particles are shaken with chloroform, provided that ATP or glycerol is present in the suspending medium. The extraction is very rapid and appears to be complete. 2. The ATPase of the chloroform extract is about 50% pure and can be readily purified to a specific activity of 60-70mumol/min per mg of protein by (NH(4))(2)SO(4) fractionation and column chromatography on Sephadex G-200. 3. The particulate and soluble ATPases have many similar properties, including their K(m) values for ATP, activation by various metal ions, hydrolytic activity with other nucleotides and stimulation by bicarbonate ions. 4. Unlike the particulate enzyme, the soluble enzyme is cold-labile and insensitive to oligomycin. 5. The molecular weight indicated by the mobility of the soluble ATPase on Sepharose 6B is 360000. 6. The soluble ATPase combines very readily with liver submitochondrial particles depleted of ATPase by salt extraction, and oligomycin-sensitivity is restored. Very little recombination of the enzyme occurs with chloroform-extracted particles. 7. The soluble enzyme contains orcinol-reactive material, suggesting that it may be a glycoprotein. The carbohydrate content was estimated to be 1-2% by weight. 8. It is concluded that the liver ATPase obtained by the chloroform extraction method of Beechey, Hubbard, Linnett, Mitchell & Munn [(1975) Biochem. J.148, 533-537] is similar to other preparations described previously and that this method is superior in simplicity and speed.

Adenosine Triphosphatases↗
PubMed1977

Transport and oxidation of choline by liver mitochondria.

1. Rapid choline oxidation and the onset of P(i)-induced swelling by liver mitochondria, incubated in a sucrose medium at or above pH7.0, required the addition of both P(i) and an uncoupling agent. Below pH7.0, P(i) alone was required for rapid choline oxidation and swelling. 2. Choline oxidation was inhibited by each of several reagents that also inhibited P(i)-induced swelling under similar conditions of incubation, including EGTA, mersalyl, Mg(2+), the Ca(2+)-ionophore A23187, rotenone and nupercaine. None of these reagents had any significant effect on the rate of choline oxidation by sonicated mitochondria. There was therefore a close correlation between the conditions required for rapid choline oxidation and for P(i)-induced swelling to occur, suggesting that in the absence of mitochondrial swelling the rate of choline oxidation is regulated by the rate of choline transport across the mitochondrial membrane. 3. Respiratory-chain inhibitors, uncoupling agents (at pH6.5) and ionophore A23187 caused a loss of endogenous Ca(2+) from mitochondria, whereas nupercaine and Mg(2+) had no significant effect on the Ca(2+) content. Inhibition of choline oxidation and mitochondrial swelling by ionophore A23187 was reversed by adding Ca(2+), but not by Mg(2+). It is concluded that added P(i) promotes the Ca(2+)-dependent activation of mitochondrial membrane phospholipase activity in respiring mitochondria, causing an increase in the permeability of the mitochondrial inner membrane to choline and therefore enabling rapid choline oxidation to occur. Nupercaine and Mg(2+) appear to block choline oxidation and swelling by inhibiting phospholipase activity. 4. Choline was oxidized slowly by tightly coupled mitochondria largely depleted of their endogenous adenine nucleotides, suggesting that these compounds are not directly concerned in the regulation of choline oxidation. 5. The results are discussed in relation to the possible mechanism of choline transport across the mitochondrial membrane in vivo and the influence of this process on the pathways of choline metabolism in the liver.

Adenine Nucleotides↗
PubMed1977

Induction of D-aldohexoside:cytochrome c oxidoreductase in Agrobacterium tumefaciens.

D-Aldohexopyranoside:cytochrome c oxidoreductase (ACO) was strongly induced by cellobiose, alpha-methylglucoside, beta-methylglucoside, kojibiose, and sophorose. Induction was rapid, and ACO was readily detectable within 10 min after addition of cellobiose as inducer. Although not measurable for 30 to 40 min after addition of inducer, once started, the rate of induction with alpha-methylglucoside equaled or even exceeded that obtained with cellobiose. Induction by sucrose, maltose, alpha-alpha-trehalose, melibiose, and lactose was weak. In general, the active ACO inducers were poor glycosidase inducers; the converse also appeared to be true. Although ACO induction was not repressed by D-glucose, it was repressed by succinate, malate, and fumarate.

Alcohol Oxidoreductases↗
PubMed1975

A protective function of superoxide dismutase during respiratory chain activity.

(1) Aerobic incubation of heart muscle submitochondrial particles in phosphate buffer after treatment with NADH causes a progressive and substantial inhibition of the NADH oxidation system. Succinate oxidation remains almost unaffected by NADH treatment. (2) The loss of NADH oxidase activity is due to an inhibition of the respiratory chain-linked NADH dehydrogenase. This inhibition of the enzyme is very similar to that caused by combination of the organic mercurial mersalyl with NADH dehydrogenase. (3) The inhibition of NADH oxidation is largely prevented by compounds that are known to react with superoxide ions (02-.), including superoxide dismutase, cytochrome c, tiron and Mn2+. EDTA also has a protective effect, but a number of other metal chelating agents, and several proteins, including catalase, are without effect. (4) It is concluded that the inhibition of NADH oxidation of NADH oxidation by superoxide ions or by mersalyl is reversible and is therefore not due to the loss of oxidoreduction components from the respiratory chain or to an irreversible change in protein conformation. (6) The function of mitochondrial superxide dismutase is discussed in relation to the key role of NADH dehydrogenase in energy-conserving reactions and the formation of hydrogen peroxide during mitochondrial oxidations.

Animals↗
PubMed1975

Polarographic assay and intracellular distribution of superoxide dismutase in rat liver.

1. A polarographic assay of superoxide (O2--) dismutase (EC 1.15.1.1) activity is described, in which the ability of the enzyme to inhibit O2---dependent sulphite oxidation, initiated by xanthine oxidase activity, is measured. The assay was used in a study of the intracellular distribution of superoxide dismutase in rat liver. Both cyanide-sensitive cupro-zinc dismutase (92% of the total activity) and cyanide-insensitive mangano-dismutase (8%) were measured. 2. Rat liver homogenates contained both particulate (16%y and soluble (84%) dismutase activity. The particulate activity contained both types of dismutase, whereas nearly all the soluble dismutase was a cupro-zinc enzymes. The distribution pattern of mangano-dismutase was similar to that of cytochrome oxidase and glutamate dehydrogenase, indicating that the enzyme was probably present exclusively in the mitochondria. 3. Superoxide dismutase activity in the heavy-mitochondrial (M) fraction was latent and was activated severalfold and largely solubilized by sonication. Treatment of the M fraction with digitonin or a hypo-osmotic suspending medium indicated that most of the cupro-zinc dismutase was located in the mitochondrial intermembrane space, whereas the mangano-enzyme was located in the inner-membrane and matrix space. 4. A small amount of dismutase activity appeared to be present in the nuclei and microsomal fraction, but little or no activity in the lysosomes or peroxisomes. 5. The results are discussed in relation to the intracellular location of known O2---generating enzymes, the possible role of superoxide dismutase activity in intracellular H2O2 formation, and to current views on the physiological function of the enzyme.

Animals↗
PubMed1971

Conditions for production of 3-ketomaltose from Agrobacterium tumefaciens.

Up to 39% yields of 3-ketomaltose were achieved in 18 to 22 hr when Agrobacterium tumefaciens NRRL B-36 was cultured at 25 to 28 C in a simple medium containing 4.0 to 8.0% maltose, 0.09% urea, 0.5% CaCO(3), 0.6% KH(2)PO(4), and 0.025% MgSO(4).7H(2)O. For maximum production of 3-ketomaltose the culture had to be maintained approximately at pH 7.0.

Bacteriological Techniques↗
PubMed1969

Evidence of a phosphate-transporter system in the inner membrane of isolated mitochondria.

1. The organic mercurial sodium mersalyl, formaldehyde, dicyclohexylcarbodiimide and tributyltin each blocked respiratory-chain-linked ATP synthesis in rat liver mitochondria. 2. Mersalyl and formaldehyde also blocked a number of other processes dependent on the entry of inorganic phosphate into mitochondria, including mitochondrial respiration and swelling stimulated by cations and phosphate, the substrate-level phosphorylation reaction of the citric acid cycle, and swelling in ammonium phosphate. 3. Dicyclohexylcarbodi-imide and tributyltin did not inhibit the entry of phosphate into mitochondria. 4. Mersalyl and formaldehyde had a relatively slight effect on succinate oxidation and swelling stimulated by cations when phosphate was replaced by acetate, on succinate oxidation stimulated by uncoupling agents, and on swelling in solutions of ammonium salts other than phosphate or arsenate. 5. Formaldehyde blocked the oxidation of NAD-linked substrates in mitochondria treated with 2,4-dinitrophenol and the ATP-dependent reduction of NAD by succinate catalysed by ox heart submitochondrial particles. Both these effects appear to be due to an inhibition by formaldehyde of the NAD-flavin region of the respiratory chain. 6. Concentrations of dicyclohexylcarbodiimide or tributyltin sufficient to abolish ADP-stimulated respiration blocked the dinitrophenol-stimulated adenosine triphosphatase activity, whereas mersalyl and formaldehyde caused only partial inhibition of ATP hydrolysis. 7. When mitochondria were incubated with dinitrophenol and ATP, less than 10% of the total inorganic phosphate liberated was recovered in the mitochondria and no swelling occurred. In the presence of mersalyl or formaldehyde at least 80% of the total inorganic phosphate liberated was retained in the mitochondria and extensive swelling was observed. This swelling was inhibited by oligomycin but not by antimycin or rotenone. 8. The addition of mersalyl to mitochondria swollen by treatment with valinomycin, K(+) and phosphate blocked the contraction induced by dinitrophenol and caused an increase in the phosphate content of the mitochondria, but had no effect on the contraction of mitochondria when phosphate was replaced by acetate. 9. It is concluded that mitochondria contain a phosphate-transporter system, which catalyses the movement of phosphate in either direction across the mitochondrial membrane, and that this system is inactivated by organic mercurials and by formaldehyde. Evidence is presented that the phosphate-transporter system is situated in the inner membrane of rat liver mitochondria and is also present in other types of mammalian mitochondria.

Acetates↗
PubMed1968

Influence of mitochondrial inhibitors on the respiration and energy-dependent uptake of iodide by thyroid slices.

The influence of mitochondrial inhibitors, including oligomycin, antimycin and rotenone, on the iodide and oxygen uptake and the nucleotide content of incubated sheep thyroid slices was investigated. Each inhibitor strongly suppressed both iodide and oxygen uptake, and decreased the nucleoside triphosphate content of the slices. In most cases the addition of glucose or mitochondrial substrates restored iodide uptake in inhibitor-treated slices. Inhibitor concentrations sufficient to inhibit iodide uptake strongly had only slight effects on the thyroidal Na(+)+K(+)-activated adenosine triphosphatase. It is concluded that the inhibitors produce their effects by the inhibition in vivo of mitochondrial oxidative phosphorylation. ATP synthesis appears to be essential for iodide uptake to occur, and the high-energy intermediates (or energized state) of oxidative phosphorylation cannot be used to energize the uptake process. To a limited extent glycolytic ATP synthesis can support iodide uptake, which is therefore not exclusively dependent on aerobic metabolism. The mechanism of energy-linked iodide uptake is discussed.

Adenosine Triphosphatases↗