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Biomedical subjects

D O Hall

Publications and source records attributed to D O Hall.

At least 19 recordsLinked to original sources
PubMed2005

The effect of Butterworth and Metz reconstruction filters on volume and ejection fraction calculations with 99Tcm gated myocardial SPECT.

This study was carried out to measure the differences produced by change of reconstruction filter in calculations of left-ventricular end-diastolic volumes, end-systolic volumes, stroke-volumes and left-ventricular ejection-fractions from (99)Tc(m) Sestamibi (Bristol-Myers Squibb) gated myocardial perfusion SPECT studies. 30 patients had gated SPECT myocardial perfusion imaging at rest. The acquired projections were separately filtered with two filters, a low-pass filter (Butterworth) and an edge-enhancement filter (Metz). Each study was then further processed to determine left-ventricular end-diastolic volume, end-systolic volume, stroke volume and ejection fraction, and to assess defect size. The results for each patient with the two filters were compared. Calculated end-diastolic volumes, end-systolic volumes and left-ventricular ejection fractions, for each filter, were well correlated. Stroke volumes showed worse correlation. The differences between left-ventricular ejection-fractions, end-diastolic volumes and end-systolic volumes were statistically significant. There was no significant difference in stroke volumes. Ejection fractions were inversely correlated with defect size, but change in ejection fraction due to filter was not. End-diastolic and end-systolic volumes were correlated with defect size, but change in volumes due to filter was not. Thus the results for changes produced by choice of filter are not dependent on defect size. Using different reconstruction pre-filters in gated myocardial perfusion SPECT significantly changes the results of calculations of physiological parameters. Each centre should be consistent in the use of filters as this may affect the clinical consequences of the result.

Adult↗
PubMed2000

Hydrogen production by Anabaena variabilis PK84 under simulated outdoor conditions.

Hydrogen production by autotrophic, vanadium-grown cells of Anabaena variabilis PK84, a cyanobacterial mutant impaired in the utilization of molecular hydrogen, has been studied under simulated outdoor conditions. The cyanobacterium was cultivated in an automated helical tubular photobioreactor (4.35 L) under air containing 2% CO(2), with alternating 12-h light (36 degrees C) and 12-h dark (14 degrees to 30 degrees C) periods. A. variabilis steadily produced H(2) directly in the photobioreactor during continuous cultivation for 2.5 months. The maximum H(2) production by the continuously aerated culture under light of 332 microE. s(-1). m(-2) was 230 mL per 12-h light period per photobioreactor and was observed at a growth density corresponding to 3.6 to 4.6 microgram Chl a. mL(-1) (1.2 to 1.6 mg dry weight. mL(-1)). Replacement of air with an argon atmosphere enhanced H(2) evolution by a factor of 2. This stimulatory effect was caused mainly by N(2) deprivation in the cell suspension. A short-term decrease of the CO(2) concentration in the air suppressed H(2) evolution. Anoxygenic conditions over the dark periods had a negative effect on H(2) production. The peculiarity of hydrogen production and some physiological characteristics of A. variabilis PK84 during cultivation in the photobioreactor under a light-dark regime are investigated.

Air↗
PubMed1999

H(2) photoproduction by batch culture of Anabaena variabilis ATCC 29413 and its mutant PK84 in a photobioreactor.

Hydrogen production by Anabaena variabilis ATCC 29413 and of its mutant PK84, grown in batch cultures, was studied in a photobioreactor. The highest volumetric H(2) production rates of native and mutant strains were found in cultures grown at gradually increased irradiation. The native strain evolved H(2) only under an argon atmosphere with the actual rate as high as the potential rate (measured in small vials under optimal conditions). In this case 61% of oxygenic photosynthesis was used for H(2) production. In contrast the mutant PK84 produced H(2) during growth under CO(2)-enriched air. Under these conditions at the maximum rate of H(2) production (10 mL h(-1) L(-1)), 13% of oxygenic photosynthesis was used for H(2) production and the actual H(2) production was only 33% of the potential. Under an atmosphere of 98% argon + 2% CO(2) actual H(2) production by mutant PK84 was 85% of the potential rate and 66% of oxygenic photosynthesis was used for H(2) production. Hydrogen production under argon + CO(2) by the mutant was strictly light-dependent with saturation at about 300 microE m(-2) s(-1). However, the rate of photosynthesis was not saturated at this irradiation. At limiting light intensities (below 250 microE m(-2) s(-1)) 33-58% of photosynthesis was used for H(2) production. Hydrogen evolution by PK84 under air + 2% CO(2) was also stimulated by light; but was not saturated at 332 microE m(-2) s(-1) and did not cease completely in darkness. The rate of oxygen photoevolution was also not saturated. A mechanism for increasing cyanobacterial hydrogen production is proposed.

Anabaena↗
PubMed1996

Effect of photoinhibition and temperature on carotenoids in sorghum leaves.

Changes in carotenoid composition, CO2 assimilation and chlorophyll fluorescence due to photoinhibition at 5 degrees C and 20 degrees C were studied in 12 day and 30 day old sorghum leaves. The old leaves had a higher violaxanthin (V) content and less beta-carotene. Photoinhibition at both temperatures caused significant increases in zeaxanthin (Z) and decreases in violaxanthin. However, in young leaves the increase in zeaxanthin was greater than the decrease in violaxanthin. In young leaves the V + A + Z pool size (A = antheraxanthin) almost doubled under photoinhibitory conditions (compared to controls) while in old leaves the V + A + Z pool remained approximately constant. After photoinhibition treatment changes in the levels of the xanthophylls were restored during a recovery period both in young and old leaves. When rephotoinhibited after a 48 hr recovery period, the young plants showed better protection against photoinhibition. We suggest that in young leaves zeaxanthin is newly synthesized under photoinhibitory conditions besides being de-epoxidized from violaxanthin and that the synthesis of V + A + Z pool is higher at 20 degrees C than at 5 degrees C in both young and old leaves.

Carbon Dioxide↗
PubMed1995

Chest physiotherapy in cystic fibrosis: a comparative study of autogenic drainage and the active cycle of breathing techniques with postural drainage.

BACKGROUND--Autogenic drainage has been suggested as an alternative method of chest physiotherapy in patients with cystic fibrosis. In this study autogenic drainage was compared with the active cycle of breathing techniques (ACBT) together with postural drainage. METHODS--Eighteen patients with cystic fibrosis took part in a randomised two-day crossover trial. There were two sessions of one method of physiotherapy on each day, either autogenic drainage or ACBT. The study days were one week apart. On each day the patients were monitored for six hours. Mucus movement was quantified by a radioaerosol technique. Airway clearance was studied qualitatively using xenon-133 scintigraphic studies at the start and end of each day. Expectorated sputum was collected during and for one hour after each session of physiotherapy. Pulmonary functions tests were performed before and after each session. Oxygen saturation (SaO2) and heart rate were measured before, during, and after each session. RESULTS--Autogenic drainage cleared mucus from the lungs faster than ACBT over the whole day. Both methods improved ventilation, as assessed by the xenon-133 ventilation studies. No overall differences were found in the pulmonary function test results, but more patients had an improved forced expiratory flow from 25% to 75% with autogenic drainage, while more showed an improved forced vital capacity with ACBT. No differences were found in sputum weight and heart rate, nor in mean SaO2 over the series, but four patients desaturated during ACBT. CONCLUSIONS--Autogenic drainage was found to be as good as ACBT at clearing mucus in patients with cystic fibrosis and is therefore an effective method of home physiotherapy. Patients with cystic fibrosis should be assessed as to which method suits them best.

Adolescent↗
PubMed1994

Different sites of photodamage in chilling-sensitive (sorghum) and chilling-resistant (barley and wheat) plants.

The electron transport chain was affected to varying degrees by high light intensity at low temperature in different crop plants. The PS II was found to be the sensitive site while PS I showed very little change in its activity. Photoinhibition affected the oxidizing side of PS II in all three plants. However, the site of inhibition was different in chilling-sensitive and chilling-resistant plants. In sorghum, the water splitting reaction was damaged while in barley and wheat the damage occurred in the reaction centre itself. It appears that photoinhibition may affect different sites within the PS II in chilling-resistant and sensitive plants.

Cold Temperature↗
PubMed1991

The synergistic effect of drought and light stresses in sorghum and pearl millet.

The effects of drought stress and high irradiance and their combination were studied under laboratory conditions using young plants of a very drought-resistant variety, ICMH 451, of pearl millet (Pennisetum glaucum) and three varieties of sorghum (Sorghum bicolor)-one drought-resistant from India, one drought-tolerant from Texas, and one drought-sensitive variety from France. CO(2) assimilation rates and photosystem II fluorescence in leaves were analyzed in parallel with photosynthetic electron transport, photosystem II fluorescence, and chlorophyll-protein composition in chloroplasts isolated from these leaves. High irradiance slightly increased CO(2) assimilation rates and electron transport activities of irrigated plants but not fluorescence. Drought stress (less than -1 megapascal) decreased CO(2) assimilation rates, fluorescence, and electron transport. Under the combined effects of drought stress and high irradiance, CO(2) assimilation rates and fluorescence were severely inhibited in leaves, as were the photosynthetic electron transport activities and fluorescence in chloroplasts (but not photosystem I activity). The synergistic or distinctive effect of drought and high irradiance is discussed. The experiments with pearl millet and three varieties of sorghum showed that different responses of plants to drought and light stresses can be monitored by plant physiological and biochemical techniques. Some of these techniques may have a potential for selection of stress-resistant varieties using seedlings.

Journal Article↗
PubMed1987

Reversible activation of hydrogenase from Escherichia coli.

Hydrogenase from Escherichia coli exhibited low activity when assayed for hydrogen:methyl viologen reductase activity and no activity when assayed for hydrogen-uptake activity with acceptors of high redox potential (dichloroindophenol, methylene blue). Nor did the enzyme as isolated catalyse proton-tritium exchange activity. Incubation under hydrogen resulted in an increase in hydrogen-uptake activity with methyl viologen and the appearance of hydrogen-uptake activity with dichloroindophenol and methylene blue. Following such treatment, the enzyme also readily catalysed isotope exchange. This process is interpreted as the conversion of the hydrogenase from an inactive 'unready' state to an 'active' state. Oxidation of active hydrogenase with dichloroindophenol caused conversion to a state resembling that of the enzyme as isolated but capable of more rapid activation under reducing conditions. This form is termed the 'ready' state. Such interconversions have been reported for hydrogenases from Desulfovibrio gigas and D. desulfuricans, and the possibility that they constitute a regulatory mechanism suggested.

Catalysis↗
PubMed1986

Differential inhibition of catalytic sites in Desulfovibrio gigas hydrogenase.

The hydrogenase of Desulfovibrio gigas has been shown to contain one nickel atom, a cluster with three irons and two clusters of the [4Fe-4S] type in an 89 kDa molecule. Though evidence that the nickel ion is involved in the site of hydrogen activation has been presented for this and other hydrogenases, the role of nickel and of the other redox centres in the protein remains to be firmly identified. We have examined the effects of inhibitors of hydrogenase activity in an attempt to identify the functions of the prosthetic redox centres. We have shown carbon monoxide to inhibit at the site of hydrogen activation. The dye, procion red, was found to compete with electron acceptors at a different site, and partial denaturation with the detergent lithium dodecyl sulphate resulted in the differential inhibition of hydrogen activation and substrate reduction. These results imply the presence of distinct domains within the protein with different catalytic activities.

Binding Sites↗
PubMed1986

Light induced H2 evolution in a hydrogenase-TiO2 particle system by direct electron transfer or via rhodium complexes.

Three different hydrogenases (isolated from Clostridium pasteurianum, Desulfovibrio desulfuricans strain Norway 4 and D. baculatus 9974) added to a suspension of TiO2 (anatase) powder are able to catalyze H2 evolution under band gap illumination of the semiconducting particles, and in the presence of EDTA or methanol as electron donor. This H2 production can be obtained by the direct electron transfer from the conduction band of the TiO2 particles to the active site of the enzyme at pHs higher than 7. This mediator-independent charge transfer is more efficient with C. pasteurianum and D. baculatus 9974 hydrogenases, and in the presence of methanol. Rhodium tris- and bis-bipyridyl complexes can act efficiently as electron carriers from the supporting particles to the adsorbed enzyme molecules in cases where the direct transfer is inefficient.

Clostridium↗
PubMed1984

Purification and properties of the soluble hydrogenase from Desulfovibrio desulfuricans (strain Norway 4).

A soluble hydrogenase has been isolated from Desulfovibrio desulfuricans (strain Norway 4) grown on Postgate's medium. The enzyme differs significantly from a membrane-bound hydrogenase previously purified from the same organism grown on Starkey's medium. The enzyme consisted of two subunits of 56 kDa and 29 kDa compared with masses of 60 kDa and 27 kDa for the membrane-bound enzyme. Analysis of preparations of the soluble enzyme by various methods gave values of 5-10 iron atoms, 6 labile sulphur atoms and 0.45-0.8 nickel atom per molecule. The enzyme was unusual in that it contained selenium, in quantities equivalent to nickel. The highly purified active enzyme produced no electron-spin-resonance (ESR) signals in the oxidized state. ESR signals due to a [3Fe-xS] cluster and nickel were observed only in some of the less active fractions of the enzyme, demonstrating that neither of these ESR-detectable components is a prerequisite for hydrogenase activity. Treatment of D. desulfuricans (Norway) cells with EDTA released a minor fraction with hydrogenase activity, which might indicate the presence of a periplasmic enzyme.

Amino Acids↗
PubMed1984

Spectroscopic studies of the nature of the iron clusters in the soluble hydrogenase from Desulfovibrio desulfuricans (strain Norway 4).

57Fe-enriched samples of the soluble hydrogenase from Desulfovibrio desulfuricans (Norway) have been investigated in both the native (oxidized) and the dithionite-reduced states using Mössbauer spectroscopy. The data clearly show that the iron in this enzyme is predominantly in the form of iron-sulphur clusters which are closely similar to the [4Fe-4S] clusters found in a large number of ferredoxins, such as that from Bacillus stearothermophilus. There appear to be two [4Fe-4S] clusters. The iron-sulphur clusters in the oxidized protein are virtually diamagnetic, as indicated by Mössbauer, electron spin resonance and magnetic circular dichroic spectroscopy. On reduction by dithionite + methyl viologen, Mössbauer spectroscopy showed that only 50% of the [4Fe-4S] clusters were reduced. Even reduction with hydrogen up to a pressure of 23 GPa did not reduce the iron-sulphur clusters completely. An ESR signal due to a rapidly relaxing species with g = 2.03, 1.89 was observed in the reduced protein, together with a weaker spectrum from a slower-relaxing species at g = 2.34, 2.12.

Chemical Phenomena↗
PubMed1984

Comparison of the properties of two hydrogenases from the photosynthetic bacterium Chromatium vinosum.

Chromatium vinosum hydrogenases I and II were purified to specific activities of 9.6 and 28.0 units/mg protein, respectively. They have the same isoelectric point (pI = 4.1), and their visible spectra are typical of iron-sulfur proteins. Hydrogenase II in general was more stable than hydrogenase I. Both enzymes lost their activities slowly during storage in air, and this inactivation was more apparent in preparations of hydrogenase I. Bovine serum albumin helped to stabilize hydrogenase I against thermal and storage inactivation. The pH optima of H2-evolution activity of hydrogenases I and II were 7.4 and 5.4, respectively. Neither enzyme was able to evolve H2 from reduced ferredoxins as the sole electron carrier, but ferredoxins had an effect on the activity with methyl viologen as carrier to hydrogenase I. None of the natural compounds tested was able to serve as a physiological donor for H2 production. Hydrogenase I was more susceptible than hydrogenase II to inhibition by heavy metal ions and other enzyme inhibitors. Both enzymes were reversibly inhibited by CO with Ki values of 12 and 6 Torr for hydrogenase I and II, respectively. Hydrogenase I was more sensitive to denaturation by urea and guanidinium chloride while hydrogenase II was more susceptible to sodium dodecyl sulfate. Both enzymes were rapidly and irreversibly inactivated by dimethyl sulfoxide. Hydrogenase I evolved H2 from methyl viologen and ferredoxin photoreduced by chloroplasts. The enzymes differed in their iron and acid-labile sulfur contents.

Air↗
PubMed1983

Kinetic studies on reactions of iron-sulphur proteins. Oxidation of the reduced form of Spirulina platensis [2Fe-2S] ferredoxin with inorganic complexes.

Kinetic results are presented for the reaction of reduced [2Fe-2S] ferredoxin from the blue-green alga Spirulina platensis with Co(NH3)6(3+), Co(edta)- and Co(acac)3 as oxidants at pH 8.0 at I0.10 (NaCl). The aim is to compare results obtained with those previously reported for the [2Fe-2S] ferredoxin from parsley, where the two ferredoxins under consideration are in evolutionary terms widely divergent (35% amino acid variations). The three oxidants chosen have different ligand sets and different charges, and are the complexes that in previous studies have given greatest diversity in behaviour. With Co(NH3)6(3+) first-order rate constants (oxidant in large excess) tend to a limiting value with increasing concentration of oxidant. With Co(edta)- and Co(acac)3 there is no similar tendency to limiting behaviour and a first-order dependence on oxidant is observed. The temperature-dependence of the Co(NH3)6(3+) reaction was investigated, and values were obtained for delta H0 [19.8kJ X mol-1 (4.7kcal X mol-1)] and delta S0 [129.3J X K-1 X mol-1 (30.9 cal X K-1 X mol-1)] for the association step that occurs before electron transfer. Whereas redox-inactive Cr(NH3)6(3+) displays competitive inhibition in the reaction of Co(NH3)6(3+), it accelerates the reaction of Co(edta)-, and only partially blocks the reaction with Co(acac)3. Results obtained are similar to those previously reported for parsley (and spinach) ferredoxin. It is concluded that electrostatics play a dominant role and that a negatively charged functional site on the protein common to all three ferredoxins is influential. Conserved negative patches at positions 67-69 and 94-96 within 1.0 nm (10A) of an Fe atom of the active site, as well as the exposed S atoms of cysteine residues 41 and 46, which are a part of the Fe2S*2(SR)4(3-) cluster, are the most likely possibilities. The various effects of Cr(NH3)6(3+) provide a means of testing for utilization of the same site in reactions of the ferredoxins with physiological partners.

Cobalt↗
PubMed1983

Purification and properties of the membrane-bound by hydrogenase from Desulfovibrio desulfuricans.

The membrane-bound hydrogenase from the anaerobic sulphate-reducing bacterium Desulfovibrio desulfuricans (Norway strain) has been purified to homogeneity, with an overall 80-fold purification and a specific activity of 70 mumol of H2 evolved/min per mg of protein. The hydrogenase had a relative molecular mass of 58 000 as determined by gel filtration and was estimated to contain six iron atoms and six acid-labile sulphur groups per molecule. The absorption spectrum of the enzyme was characteristic of an iron-sulphur protein. The E400 and E280 were 28 500 and 109 000 M-1.cm-1 respectively. The e.s.r. of the oxidized protein indicated the presence of [4Fe-4S]3+ or [3Fe-3S]3+, and another paramagnetic centre, probably Ni(III). The hydrogenase was inhibited by heavy-metal salts, carbon monoxide and high ionic strength. However, it was resistant to inhibition by thiol-blocking and metal-complexing reagents. N-Bromosuccinimide totally inhibited the enzyme activity at low concentrations. The enzyme was stable to O2 over long periods and to high temperatures. It catalyses both H2-evolution and H2-uptake with a variety of artificial electron carriers. D. desulfuricans cytochrome C3, its natural electron carrier, had a high affinity for the enzyme (Km = 2 microns). Rate enhancement was observed when cytochrome C3 was added to Methyl Viologen in the H2-evolution assay. The pH optimum for H2-evolution was 6.5.

Amino Acids↗
PubMed1982

Ascorbate as a substrate for photoproduction of hydrogen by photosystem I of chloroplasts.

The photoproduction of hydrogen by 2-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-inhibited chloroplasts from ascorbate under anaerobic conditions was studied in the pH range 5.0 to 7.5 using methyl viologen (MV), N,N,N',N'-tetramethyl-P-phenylenediamine (TMPD), and excess hydrogenase from Desulfovibrio desulfuricans. (a) At neutral and basic pHs, the photoreduction of MV, which reacted back with photoxidized ascorbate (dehydroascorbate [DHASC]), and the rates of H(2) photoproduction were very low. The slow H(2) photoproduction was explained by the reversible reduction of MV by the photoproduced H(2) (catalyzed by hydrogenase) and its reoxidation by DHASC resulting in H(2) uptake. (b) At pH 5.2, relatively high initial rates of H(2) photoproduction were obtained, which were comparable to the rates of O(2) consumption at pH 5.2 by photosystem I (catalyzed by photoreduced MV). However, accumulation of photoreduced MV under anaerobic conditions was not detected. In the presence of high concentrations of protons, the H(2) uptake by DHASC was very slow because the equilibrium concentration of H(2)-reduced MV was very small, thus allowing H(2) evolution mediated by photoreduced MV to compete with the back reaction with DHASC. (c) The continuous accumulation of DHASC, which was generated together with H(2), gradually slowed the H(2) evolution until it stopped after about 3 hours. At high concentrations, DHASC was able to compete with the coupling of photoreduced MV to hydrogenase and H(2) evolution. (d) Dithiothreitol (DTT) reduced the DHASC and consequently competed with the back reaction of the photoreduced and H(2)-reduced MV with DHASC. DTT thus prolonged the time period of H(2) photoproduction from ascorbate and abolished the dependence of its rate on pH in the range of 5.2 to 7.5 (e) A study of H(2) uptake by chemically oxidized ascorbate (in the dark) showed that MV and hydrogenase were both required to catalyze electron transfer from H(2) to DHASC. TMPD prevented this H(2) consumption by DHASC (in a chloroplast reaction mixture containing MV and hydrogenase). Illumination restored the H(2) uptake presumably by generating reduced MV which activated the hydrogenase.

Journal Article↗