Search PubMed⌕ Search

Biomedical subjects

M B Cooper

Publications and source records attributed to M B Cooper.

At least 37 records · Page 2Linked to original sources
PubMed1986

Citrate interference with the determination of acetylcarnitine: a method for its elimination.

Citrate can interfere with the determination of acetylcarnitine when measured by a radioisotopic method. In this report we present a modified procedure designed to avoid this effect. Recovery of added acetylcarnitine was approximately 95%. Acetylcarnitine in normal human plasma was found to range from 0.8 to 19.9 nmol/ml with a mean of 6.3; that of human skeletal muscle ranged from 0.1 to 1.6 nmol/mg protein with a mean of 1.08. The results confirm that exercise gives rise to increased acetylcarnitine content of plasma.

Acetylcarnitine↗
PubMed1986

The effect of marathon running on carnitine metabolism and on some aspects of muscle mitochondrial activities and antioxidant mechanisms.

Carnitine is an essential co-factor in the catabolism of fats as an energy source. The primary purpose of this study was to investigate the effect of running a marathon on the metabolism of carnitine by endurance-trained athletes, and to evaluate the effect of carnitine administration on the performance of such exercise. The effects of marathon running on mitochondrial enzymes and cellular anti-oxidants were also examined to assess whether the expression of these activities is altered by exercise. Subjects were 10 experienced male marathon runners aged between 19 and 25 years. Running a marathon caused a fall in the plasma content of unesterified carnitine (37%) and an increase in the level of acetylcarnitine present (288%). Loading of the athletes with L-carnitine for 10 days before running a marathon abolished the exercise-induced fall in plasma-free carnitine (P less than 0.05) whilst amplifying the production of acetylcarnitine (P less than 0.05). Carnitine loading of the athletes studied made no detectable improvement in performance of the marathon (P greater than 0.05). Cytochrome oxidase, succinate cytochrome C reductase and superoxide dismutase activities present in skeletal muscle were unaltered by marathon running. However, such exercise caused a large increase in the tissue content of oxidized glutathione (189%) at the expense of reduced glutathione (-18%).

Acetylcarnitine↗
PubMed1985

Shock-induced damage to mitochondrial function and some cellular antioxidant mechanisms in humans.

The effects of circulatory shock on skeletal muscle mitochondrial oxidative activity in various substrates and cytochrome oxidase activity have been investigated using samples of muscle obtained by the needle biopsy technique from human subjects. The effect of shock on superoxide dismutase activity and glutathione content of skeletal muscle was also examined. The results show that there is a large decrease in cytochrome oxidase activity during shock and also in the capacity of the mitochondria to oxidize either succinate, or pyruvate, or palmitoyl carnitine. There is a fall in the tissue content of superoxide dismutase and in the total glutathione present. Furthermore, an increased oxidized glutathione content causes a decrease in the molar ratio of reduced to oxidized glutathione present in the muscle. These findings suggest that mitochondrial electron transport chain (ETC) oxidative damage can play a relevant role in the pathogenesis of circulatory shock and support the hypothesis of oxygen-free radical involvement in the cellular injury.

Biopsy, Needle↗
PubMed1985

Effects of L-carnitine administration on mitochondrial electron transport activity present in human muscle during circulatory shock.

Carnitine was administered to a group of patients in shock, and the activities of cytochrome oxidase and succinate cytochrome c reductase in muscle needle biopsies from these patients were compared to those activities present in a non-carnitine treated control group of patients. Carnitine seemingly exerted a significant protective action on cytochrome oxidase activity during the initial phases of shock, but not to such an extent on succinate cytochrome c reductase activities.

Carnitine↗
PubMed1982

The effect of superoxide generation on the ability of mitochondria to take up and retain Ca2+.

When heart or liver mitochondria are exposed to superoxide radicals generated from xanthine + xanthine oxidase their ability to take up and to retain Ca2+ is impaired. The rate of oxidation of pyruvate + malate as substrates is diminished and the appearance of thiol groups when the mitochondria are supplied with these substrates is abolished. These inhibitory effects are offset if respiration is supported by succinate in presence of rotenone provided that a substrate (beta-hydroxybutyrate) is provided to maintain the reduction of NADH. The data agree with the thesis that a generation of thiol groups is essential to maintain membrane integrity and that the generation depends on provision of reduced NAD(P)H.

Animals↗
PubMed1982

Monoamine oxidase activity of mitochondria prepared from rat liver and rat heart.

The effect of agents that change the respiratory state of the mitochondrion on tyramine oxidation was investigated. Neither uncoupler nor ADP and P1 in the presence of substrate produced any change in the rate of tyramine oxidation, as judged by direct measurement of tyramine oxidation or by H2O2 production. We conclude that previously reported depression of monoamine oxidase activity by stimulated respiration was due to oxygen depletion.

Animals↗
PubMed1981

The use of proteinases to determine the topological location of cytochrome P-450 in vesicles derived from smooth endoplasmic reticulum of rat liver.

1. The phospholipid bilayer of intact vesicles from smooth endoplasmic reticulum is impermeable to macromolecules. Specific and non-specific proteinases were used to investigate the site of membrane proteins in the transverse plane of the bilayer. 2. When two proteinases were used in conjunction, denaturing effects additional to proteolysis were observed on cytochrome P-450 content and glucose 6-phosphatase activity which did not depend on the integrity of the phospholipid bilayer. 3. When lipid peroxidation was inhibited, these effects were not observed.

Animals↗
PubMed1981

Newly biosynthesized cytochrome P-450 associated with the golgi apparatus from livers of rats induced with phenobarbital.

1. Cytochrome P-450 has been detected in preparations of golgi apparatus from the livers of phenobarbital-induced rats. 2. Newly biosynthesized cytochrome P-450 is also present in preparations of golgi apparatus. By using three different techniques to fractionate the golgi into vesicle contents and membrane components it was found that newly biosynthesized cytochrome P-450 is associated solely with the membrane fraction. 3. By investigating the susceptibility of cytochrome P-450, present in the golgi apparatus, to the action of trypsin it was found that the majority was oriented on the cytosolic face of the membrane.

Animals↗
PubMed1980

Asymmetric distribution of cytochrome P-450 and NADPH--cytochrome P-450 (cytochrome c) reductase in vesicles from smooth endoplasmic reticulum of rat liver.

1. The topography of cytochrome P-450 in vesicles from smooth endoplasmic reticulum of rat liver has been examined. Approx. 50% of the cytochrome is directly accessible to the action of trypsin in intact vesicles whereas the remainder is inaccessible and partitioned between luminal-facing or phospholipid-embedded loci. Analysis by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis reveals three major species of the cytochrome. Of these, the variant with a mol.wt. of 52000 is induced by phenobarbitone and this species is susceptible to trypsin. 2. After trypsin treatment of smooth membrane, some NADPH-cytochrome P-450 (cytochrome c) reductase activity remains and this remaining activity is enhanced by treatment with 0.05% deoxycholate, which renders the membranes permeable to macromolecules. In non-trypsin-treated control membranes the reductase activity is increased to a similar extent. These observations suggest an asymmetric distribution of NADPH-cytochrome P-450 (cytochrome c) reductase in the membrane. 3. As compared with dithionite, NADPH reduces only 44% of the cytochrome P-450 present in intact membranes. After tryptic digestion, none of the remaining cytochrome P-450 is reducible by NADPH. 4. In the presence of both a superoxide-generating system (xanthine plus xanthine oxidase) and NADPH, all the cytochrome P-450 in intact membrane (as judged by dithionite reducibility) is reduced. The cytochrome P-450 remaining after trypsin treatment of smooth vesicles cannot be reduced by this method. 5. The superoxide-dependent reduction of cytochrome P-450 is prevented by treatment of the membranes with mersalyl, which inhibits NADPH-cytochrome P-450 (cytochrome c) reductase. Thus the effect of superoxide may involve NADPH-cytochrome P-450 reductase and cytosolically orientated membrane factor(s).

Animals↗
PubMed1979

The role of components of the endoplasmic reticulum in the biosynthesis of cytochrome P-450.

1. Antibodies have been prepared to rat hepatic cytochrome P-450 and their specificity demonstrated. These antibodies have been used to investigate the biosynthesis of cytochrome P-450 in vitro and in situ in various components of the endoplasmic reticulum. 2. A preparation of heavy rough endoplasmic reticulum translocates proteins newly biosynthesized in vitro vectorially into the luminal space and these are released by low concentrations of deoxycholate. A significant proportion of the radioactivity found in this released fraction is incorporated into cytochrome P-450. 3. Following incorporation of [14C]leucine by perfused rat liver, radioactively labelled cytochrome P-450 can be found in the intrascisternal content of heavy rough, light rough and smooth endopalsmic reticulum and also in a solublized Golgi preparation. 4. We suggest that at least part of the newly biosynthesized cytochrome P-450 is translocated into the intracisternal space of the rough endoplasmic and then passes through the other components of the endoplasmic reticulum before insertion at its ultimate membrane locus.

Animals↗
PubMed1979

Reader preference for report typefaces.

A postal survey of typeface preference is described. The survey was designed to help in the choice of typeface to be used for the internal technical Reports produced by the Post Office Research Department. Type setting for these Reports is carried out using an IBM Selectric Composer for which seven typefaces suitable for reports are available. One hundred and twenty-five people who regularly receive copies of these Reports and 57 Trainee Technicians (Apprentices) were asked to arrange these seven typefaces in order of preference and record this ranking on a response sheet. About 85% of both groups returned response sheets for statistical analysis. The results showed a significant preference for three of the typefaces: Press Roman, Theme and Univers. Of these, Press Roman is used for the text of Research Department Reports and Univers is used on diagrams and tables.

Journal Article↗
PubMed1979

The effect of feedback on keying performance.

The introduction of new telephone signalling systems and new technologies for telephone keypads has stimulated interest in the effect of providing electronic feedback on keying performance. An experiment using a conventional keypad is reported which shows that electronic auditory feedback had no significant effect on keying speed, accuracy or subject's opinion. A further series of experiments investigating the best type of feedback to improve performance with 'touch' keypads is then described. It was found that an electronic tone presented through the telephone earpiece was the best feedback. Finally, performance with two types of touch keyphones incorporating the optimum form of feedback was compared with performance using a conventional keyphone. It was found that accuracy was significantly greater with the conventional keyphone, although performance with the touch keypads could be improved by electronically removing some of the very short spurious signalling times produced by them.

Journal Article↗
PubMed1979

Controls for remote-controlled zoom lenses.

Experiments were conducted to investigate the expectation of members of the public of the relationship between a pair of pushbuttons, a rocker switch and the direction-of-zoom of a remote-controlled zoom lens. In neither case was a population stereotype found. Relatively large numbers of subjects suggested Zoom In/Zoom Out or Close-up/ Distant as labels for the zoom control buttons. A significant stereotype was demonstrated in a second experiment with a novel concentric button arrangement designed to embody the concepts apparent in the suggested labels.

Journal Article↗