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Biomedical subjects

A T Diplock

Publications and source records attributed to A T Diplock.

At least 91 records · Page 5Linked to original sources
PubMed1973

Studies on selenium incorporation into, and electron-transfer function of, liver microsomal fractions from normal and vitamin E-deficient rats given phenobarbitone.

1. The incorporation of (75)Se from Na(2) (75)SeO(3) into the liver endoplasmic reticulum of rats given phenobarbitone was investigated by using a zonal centrifuge technique. 2. It was found that, in rats deprived of vitamin E, or of vitamin E and selenium, phenobarbitone was without effect on the incorporation of (75)Se or on its conversion to (75)Se(2-). When vitamin E was given at the same time as the phenobarbitone and (75)Se, there was a large increase in the amount of (75)Se and (75)Se(2-) found in the smooth reticulum. It is concluded that there may be a specific vitamin E-dependent role for selenium and selenide in the smooth endoplasmic reticulum, and it is suggested, in the light of these and other observations, that the selenide may form a part of the active centre of a non-haem iron-containing protein ;X', that may function in microsomal electron transport. 3. Measurements of the contents of cytochromes P-450 and b(5) in liver microsomal fractions of rats given vitamin E-deficient, and vitamin E- and selenium-deficient diets, showed that haemoprotein biosynthesis is unimpaired in these rats and phenobarbitone treatment resulted in the expected increase in the haemoproteins. 4. When the reduction of cytochrome P-450 by NADH and NADPH was measured, no difference was found between normal and deficient animals. 5. These results are discussed in relation to current knowledge of microsomal electron transfer.

Animals↗
PubMed1971

The effect of vitamin E on the oxidation state of selenium in rat liver.

1. (75)Se as Na(2) (75)SeO(3) was administered orally to rats under different nutritional conditions. 2. The selenium found in the liver subcellular organelle fractions was present in at least three oxidation states: acid-volatile selenium, assumed to be selenide, zinc-hydrochloric acid-reducible selenium, assumed to be selenite, and higher oxidation states of selenium and organic derivatives, called selenate for convenience. 3. The proportion of the total selenium present as selenide present as selenide is susceptible to oxidation in vitro, which can be prevented by the addition of antioxidants in vitro. 4. The proportion of selenide is also directly related to the vitamin E status of the rats, and treatment of vitamin E-deficient rats with vitamin E results in an increase in the proportion of selenide. 5. Freezing the liver in situ before preparation of the organelle fractions did not alter the susceptibility of the selenide proportion to dietary vitamin E, indicating that the observed effects occur in vivo and not as a result of oxidation post mortem. 6. Intravenous administration of Na(2) (75)SeO(3), to rats whose alimentary tract was partially sterilized by neomycin treatment, gave a similar result to that in paragraph 4, indicating that the reduction of selenite to selenide probably occurs in vivo, and that intestinal micro-organisms are not responsible. 7. Treatment of vitamin E-deficient rats with silver produced a fall in the total (75)Se content of the liver, an effect only partially reversed by vitamin E administration. The proportion of the total selenium present as selenide was also lowered by the treatments with silver, and vitamin E significantly reversed this trend in most cases. 8. These results are consistent with the hypothesis that the active form of Se may be selenide and that the selenide may form part of the active centre of an uncharacterized class of catalytically active non-haem-iron proteins that are protected from oxidation in vivo by vitamin E.

Animals↗
PubMed1971

The effect of vitamin E on the intracellular distribution of the different oxidation states of selenium in rat liver.

1. The liver intracellular distribution of (75)Se, (75)Se(2-) and (75)SeO(3) (2-) formed from orally administered Na(2) (75)SeO(3) was studied in rats given four different dietary treatments. 2. Subcellular fractionation was done by using sucrose density gradients in a B XIV zonal centrifuge rotor, and conditions were established so that separation of lysosomal, mitochondrial, smooth- and rough-surfaced endoplasmic reticulum, and soluble fractions was achieved. 3. Marker enzymes acid phosphatase, succinate-2 - p - iodophenyl - 3 - p -nitrophenyl - 5 - phenyltetrazolium reductase and glucose 6-phosphatase were used, together with electron microscopy, to establish the identity of the fractions. 4. The dietary treatments investigated were: (a) vitamin E-deficient diet for 3 months, re-fed with vitamin E during the terminal 5 days; (b) vitamin E-deficient diet; (c) adequate diet; (d) vitamin E- and selenium-deficient diet, re-fed with vitamin E during the terminal 5 days. 5. In adequately fed rats, selenide was particularly associated with the mitochondrial fractions; in vitamin E-deficient rats, little selenide was found and the buoyant density of the mitochondria was increased, whereas re-feeding with vitamin E showed a restoration of the normal pattern. In vitamin E- and selenium-deficient rats, re-fed with vitamin E, there was no tendency for selenide to be localized in the mitochondria. 6. In the microsomal regions of the gradients, adequately fed rats showed a concentration of selenide, particularly in the smooth endoplasmic reticulum fractions, and to a lesser extent in the rough endoplasmic reticulum fractions. This was not observed in vitamin E-deficient rats, and the normal pattern was restored on re-feeding with vitamin E, both in rats given the vitamin E-deficient diet and the vitamin E- and selenium-deficient diet. 7. Some selenide was also found in the soluble fractions, when vitamin E was present, and a substantial proportion of this selenide was found to pass through a dialysis membrane. 8. These results are taken to support our hypothesis that the active form of selenium may be selenide located in non-haem iron-containing proteins, and that the function of vitamin E may be to protect the selenide from oxidation.

Animals↗
PubMed1967

The ubiquinone content of animal tissues. A survey of the occurrence of ubiquinone in vertebrates.

1. A method was developed for the analysis of ubiquinone in animal tissues and the recovery of added ubiquinone tested in liver of the rat, Crocodylus porosus and Squalus acanthias. 2. The ubiquinone content of heart, liver and gut (or breast muscle in birds) was measured in 67 different animal species, selected to be representative of all the vertebrate classes. 3. The suggestion is advanced that the possession of appreciable amounts of endogenous tissue ubiquinone is usually characteristic of evolutionarily advanced vertebrates, and the biological and biochemical significance of the results is discussed.

Animals↗