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Biomedical subjects

W A Hamilton

Publications and source records attributed to W A Hamilton.

At least 19 recordsLinked to original sources
PubMed1998

Bioenergetics of sulphate-reducing bacteria in relation to their environmental impact.

The cellular physiology of the sulphate-reducing bacteria, and of other sulphidogenic species, is determined by the energetic requirements consequent upon their respiratory mode of metabolism with sulphate and other oxyanions of sulphur as terminal electron acceptors. As a further consequence of their, relatively, restricted catabolic activities and their requirement for conditions of anaerobiosis, sulphidogenic bacteria are almost invariably found in nature as component organisms within microbial consortia. The capacity to generate significant quantities of sulphide influences the overall metabolic activity and species diversity of these consortia, and is the root cause of the environmental impact of the sulphidogenic species: corrosion, pollution and the souring of hydrocarbon reservoirs.

Energy Metabolism↗
PubMed1983

Axillofemoral and femorofemoral grafts: a 6-year experience with emphasis on the relationship of peroperative flow measurement to graft survival.

Over a 6-year period 64 axillofemoral bypass and femorofemoral crossover grafts have been performed in 58 patients, most of whom were considered unfit for intra-abdominal surgery. Indications were peripheral ischaemia in 78 per cent and disabling claudication in 22 per cent. The limb salvage rate at 3 years was 75 per cent. No claudicants lost limbs, but only one-third of patients presenting with forefoot gangrene or ulceration avoided amputation. Most patients presenting with ischaemic symptoms at rest had associated femoropopliteal and distal disease, confirmed by the ankle pressure index measurements, and this influenced graft patency. Although the cumulative patency at 3 years for all grafts combined was 57 per cent with similar patencies for both the axillofemoral and femorofemoral grafts, early occlusion was more common in axillofemoral grafts and this may be reduced in bifemoral grafts by the increased flow rate in the vertical limbs. Peroperative electromagnetic flowmeter measurements were made after reconstruction on 55 femoral arteries in 46 of the patients and graft flow velocities were derived from these measurements. Comparison between velocities from those grafts remaining patent and those subsequently occluding showed a high incidence of occlusion in grafts with a maximal velocity after distal vasodilatation of less than 8 cm/s. Graft occlusion after the first postoperative month was more commonly associated with other factors such as continued smoking, severity of distal disease and perigraft infection.

Aged↗
PubMed1983

On-line analysis of the femoral artery flow velocity waveform and its application in the diagnosis of arterial disease.

Analysis of the instantaneous peak velocity waveform obtained from the common femoral artery can be used to provide an objective assessment of arterial disease in the leg. The calculation of waveform indices pulsatility index and rise time together with principal component analysis has been found to be the ideal method by which to assess the flow data on-line.

Blood Flow Velocity↗
PubMed1980

Quantitative analysis of proton-linked transport system. beta-Galactoside exit in Escherichia coli.

The exit of lactose and thiomethyl-beta-D-galactoside from Escherichia coli ML308-225 has been studied to determine the role of carrier-dependent (zero-trans efflux) and carrier-independent (leak) processes. On the basis of its sensitivity to p-chloromercuribenzene sulphonate the exit of lactose was found to be almost wholly mediated by the carrier. Consistent with this conclusion was the finding that the rate of exit of this sugar was dependent on the external pH, being considerably slower at acid pH. On the other hand exit of thiomethyl-beta-D-galactoside was found to be composed of both carrier-dependent and carrier-independent processes. Both processes exhibited first-order kinetics with the rate constants for zero-trans efflux and leak being 0.137 min-1 and 0.079 min-1, respectively. The relevance of these findings for out earlier proposal for the methods of attenuation of solute accumulation is discussed [Booth, Mitchell & Hamilton (1979) Biochem. J. 182, 687--696].

4-Chloromercuribenzenesulfonate↗
PubMed1979

Quantitative analysis of proton-linked transport systems. Glutamate transport in Staphylococcus aureus.

1. The magnitude of the protonmotive force in respiring Staphylococcus aureus was measured over the range of extracellular pH from 5.6 to 7.8. 2. The membrane potential remains constant at 150 mV, inside-negative, but the pH gradient decreases from 2.1 units, inside-alkaline, at pH 5.6 to zero at pH 7.5 and above. 3. The accumulation of glutamate in the soluble cell pool is pH-independent at a value equivalent to 100 mV. 4. The results of experiments studying co-transport of protons are consistent with a proton/glutamate stoichiometry of 2 and electrogenic transport across the pH range examined. 5. The amount of glutamate uptake is the result of a kinetic steady state between influx and efflux pathways. 6. Evidence is presented for the regulation of this kinetic steady state by the response of the initial rate of uptake to changes in the protonmotive force.

Biological Transport↗
PubMed1979

Quantitative analysis of proton-linked transport systems. The lactose permease of Escherichia coli.

Evidence is presented that lactose uptake into whole cells of Escherichia coli occurs by symport with a single proton over the range of external pH 6.5--7.7. The proton/lactose stoicheiometry has been measured directly over this pH range by comparison of the initial rates of proton and lactose uptake into anaerobic resting cell suspensions of E. coli ML308. Further, the relationship between the protonmotive force and lactose accumulation has been studied in E. coli ML308-225 over the range of external pH 5.9--8.7. At no point was the accumulation of the beta-galactoside in thermodynamic equilibrium with the protonmotive force. It is concluded that the concentration of lactose within the cell is governed by kinetic factors rather than pH-dependent changes in the proton/substrate stoicheiometry. The relevance of these findings to the model of pH-dependent proton/substrate stoicheiometries derived from studies with E. coli membrane vesicles is discussed.

Biological Transport↗
PubMed1976

Magnitude of the protonmotive force in respiring Staphylococcus aureus and Escherichia coli.

The membrane potential and pH gradient developed across the plasma membranes of whole cells of Staphylococcus aureus and spheroplasts of Escherichia coli were estimated. The distributions of potassium ions in the presence of valinomycin and the pH gradient across the membrane were determined from the changes in pK and pH observed in the external medium during transition from the energized respiring state to the de-engerized resting condition. The protonmotive force in respiring cells was estimated at 211 mV for S. aureus and 230 mV for E. coli at external pH values of approximately 6.5. The adequacy of these protonmotive forces as a driving force for substrate accumulation or adenosine 5'-triphosphate synthesis is discussed.

Adenosine Triphosphate↗