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Biomedical subjects

D S Clark

Publications and source records attributed to D S Clark.

At least 73 records · Page 4Linked to original sources
PubMed1992

High-pressure, high-temperature bioreactor for comparing effects of hyperbaric and hydrostatic pressure on bacterial growth.

We describe a high-pressure reactor system suitable for simultaneous hyperbaric and hydrostatic pressurization of bacterial cultures at elevated temperatures. For the deep-sea thermophile ES4, the growth rate at 500 atm (1 atm = 101.29 kPa) and 95 degrees C under hydrostatic pressure was ca. three times the growth rate under hyperbaric pressure and ca. 40% higher than the growth rate at 35 atm.

Bacteria↗
PubMed1992

A mechanistic study on the enhancement of corneal penetration of phenylephrine by flurbiprofen in the rabbit.

The effect of flurbiprofen on the corneal penetration of phenylephrine was investigated using isolated albino rabbit corneas mounted in the Ussing diffusion chamber. The corneal penetration of phenylephrine was increased 5-11 times by 4-16 mM flurbiprofen. Such an increase in the corneal penetration of phenylephrine by flurbiprofen appeared to correlate with the increase in the lipophilicity of phenylephrine by flurbiprofen due to ion pair formation. The magnitude of increase at 16 mM flurbiprofen was 2.4 times less than that afforded by 0.5% EDTA and 16.3 times less than that afforded by deepithelizing the cornea. Since flurbiprofen also increased the corneal penetration of benzoic acid and sorbitol with which it cannot form ion pairs, increased lipophilicity of phenylephrine due to ion pair formation with flurbiprofen was unlikely to be the only mechanism that enhanced corneal penetration. An additional mechanism under our experimental conditions of prolonged exposure of the cornea to the phenylephrine-flurbiprofen combination was lowering of the barrier function of the corneal epithelium by concentrations of flurbiprofen greater than that used therapeutically.

Animals↗
PubMed1991

Inhibition of dextransucrase by alpha-D-glucose derivatives.

alpha-D-Glucopyranosyl fluoride was modified at positions 2, 3, or 5 and these analogs were tested as substrates and inhibitors of dextransucrase from Leuconostoc mesenteroides B-512F. The analogs studied were 2-deoxy-2-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-thio-alpha-D-glucopyranosyl fluoride, and 5-thio-alpha-D-glucopyranosyl fluoride. Kinetic constants for alpha-D-glucopyranosyl fluoride were also determined. None of the alpha-D-glucopyranosyl fluorides were accepted as substrates for dextransucrase. 2-Deoxy-2-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-fgluoro-alpha-D-glucopyranosyl fluoride, and 3-deoxy-3-thio-alpha-D-glucopyranosyl fluoride were competitive inhibitors with Ki values of 63, 93, and 53 mM, respectively. The Km for alpha-D-glucopyranosyl fluoride was found to be 26 mM. The data indicate that the hydroxyl groups at C2 and C3 are important for proper binding of alpha-D-glucopyranosyl fluoride for the active site of dextransucrase and that the C3-hydroxyl probably acts as a hydrogen-bond donor.

Binding, Competitive↗
PubMed1991

Effects of hyperbaric pressure on a deep-sea archaebacterium in stainless steel and glass-lined vessels.

The effects of hyperbaric helium pressures on the growth and metabolism of the deep-sea isolate ES4 were investigated. In a stainless steel reactor, cell growth was completely inhibited but metabolic gas production was observed. From 85 to 100 degrees C, CO(2) production proceeded two to three times faster at 500 atm (1 atm = 101.29 kPa) than at 8 atm. At 105 degrees C, no CO(2) was produced until the pressure was increased to 500 atm. Hydrogen and H(2)S were also produced biotically but were not quantifiable at pressures above 8 atm because of the high concentration of helium. In a glass-lined vessel, growth occurred but the growth rate was not accelerated by pressure. In most cases at temperatures below 100 degrees C, the growth rate was lower at elevated pressures; at 100 degrees C, the growth rates at 8, 250, and 500 atm were nearly identical. Unlike in the stainless steel vessel, CO(2) production was exponential during growth and continued for only a short time after growth. In addition, relatively little H(2) was produced in the glass-lined vessel, and there was no growth or gas production at 105 degrees C at any pressure. The behavior of ES4 as a function of temperature and pressure was thus very sensitive to the experimental conditions.

Journal Article↗
PubMed1991

Engineering considerations for the application of extremophiles in biotechnology.

Biotechnology may soon take greater advantage of extremophiles--microorganisms that grow in high salt or heavy metal concentrations, or at extremes of temperature, pressure, or pH. These organisms and their cellular components are attractive because they permit process operation over a wider range of conditions than their traditional counterparts. However, extremophiles also present a number of challenges for the development of bioprocesses, such as slow growth, low cell yield, and high shear sensitivity. Difficulties inherent in designing equipment suitable for extreme conditions are also encountered. This review describes both the advantages and disadvantages of extremophiles, as well as the specialized equipment required for their study and application in biotechnology.

Amino Acid Sequence↗
PubMed1990

A nuclear magnetic resonance technique for determining hybridoma cell concentration in hollow fiber bioreactors.

We have developed a technique for determining cell concentration in a hollow fiber bioreactor based on 23Na nuclear magnetic resonance (NMR) spectroscopy. Cell concentrations determined with this method agreed closely with concentrations calculated from 31P NMR nucleoside triphosphate (NTP) measurements and oxygen consumption rate measurements. Oxygen transfer limitations, which can complicate cell mass determinations based on oxygen consumption rates, were shown to be negligible for the bioreactor used. Specific antibody production rates in hollow fiber culture, calculated from these cell number estimates, were similar to those found in suspension culture for this cell line.

Animals↗
PubMed1990

Partial Purification and Characterization of Two Hydrogenases from the Extreme Thermophile Methanococcus jannaschii.

F(420)-nonreactive and F(420)-reactive hydrogenases have been partially purified from Methanococcus jannaschii, an extremely thermophilic methanogen isolated from a submarine hydrothermal vent. The molecular weights of both hydrogenases were determined by native gradient electrophoresis in 5 to 27% polyacrylamide gels. The F(420)-nonreactive hydrogenase produced one major band (475 kilodaltons), whereas the F(420)-reactive hydrogenase produced two major bands (990 and 115 kilodaltons). The F(420)-nonreactive hydrogenase consisted of two subunits (43 and 31 kilodaltons), and the F(420)-reactive hydrogenase contained three subunits (48, 32, and 25 kilodaltons). Each hydrogenase was active at very high temperatures. Methyl viologen-reducing activity of the F(420)-nonreactive hydrogenase was maximal at 80 degrees C but was still detectable at 103 degrees C. The maximum activities of F(420)-reactive hydrogenase for F(420) and methyl viologen were measured at 80 and 90 degrees C, respectively. Low but measureable activity toward methyl viologen was repeatedly observed at 103 degrees C. Moreover, the half-life of the F(420)-nonreactive hydrogenase at 70 degrees C was over 9 h, and that of the F(420)-reactive enzyme was over 3 h.

Journal Article↗
PubMed1989

A comparison of three radiofrequency coils for NMR studies of conductive samples.

Three rf coil designs of equal volume (approximately 15 ml) were compared using conductive samples. Magnetic loss into the sample was the dominant noise source. At physiological conductivity the sensitivity of the horizontally aligned solenoid and loop-gap resonator was only 1.3 +/- 0.2 times that of the vertically aligned slotted tube resonator.

Equipment Design↗
PubMed1988

Cholesterol aggregation and interaction with cholesterol oxidase in supercritical carbon dioxide.

High-pressure EPR spectroscopy indicates that cholesterol forms aggregates in supercritical carbon dioxide. In pure carbon dioxide, changes in cholesterol aggregate size or packing structure are observed with changing pressure. Near the critical point of carbon dioxide, cholesterol solubility is too low to permit significant aggregation, and monomeric cholesterol is observed. Addition of small amounts of dopants to supercritical carbon dioxide strongly affects cholesterol aggregation. Branched butanols (2-methyl-1-propanol and 2-methyl-2-propanol) and ethanol (to a lesser degree) promote cholesterol aggregation, while methanol, acetone, and 1-butanol do not. Cosolvents that promote aggregation also increase the rate at which cholesterol oxidase from Gloeocysticum chrysocreas catalyzes the oxidation of cholesterol. In supercritical carbon dioxide solutions, the EPR spectroscopy reveals little or no conformational change in cholesterol oxidase as 2-methyl-2-propanol or methanol is added. Damp cholesterol oxidase binds multiple cholesterol molecules; dry enzyme loses the ability to bind cholesterol. When molecular oxygen is the oxidizing agent, the rate of enzymatic cholesterol oxidation is greatly reduced in bone-dry carbon dioxide compared to that in water-saturated carbon dioxide.

3-Hydroxysteroid Dehydrogenases↗
PubMed1988

Pressure and Temperature Effects on Growth and Methane Production of the Extreme Thermophile Methanococcus jannaschii.

The marine archaebacterium Methanococcus jannaschii was studied at high temperatures and hyperbaric pressures of helium to investigate the effect of pressure on the behavior of a deep-sea thermophile. Methanogenesis and growth (as measured by protein production) at both 86 and 90 degrees C were accelerated by pressure up to 750 atm (1 atm = 101.29kPa), but growth was not observed above 90 degrees C at either 7.8 or 250 atm. However, growth and methanogenesis were uncoupled above 90 degrees C, and the high-temperature limit for methanogenesis was increased by pressure. Substantial methane formation was evident at 98 degrees C and 250 atm, whereas no methane formation was observed at 94 degrees C and 7.8 atm. In contrast, when argon was substituted for helium as the pressurizing gas at 250 atm, no methane was produced at 86 degrees C. Methanogenesis was also suppressed at 86 degrees C and 250 atm when the culture was pressurized with a 4:1 mix of H(2) and CO(2), although limited methanogenesis did occur when the culture was pressurized with H(2).

Journal Article↗
PubMed1985

Measures of knowledge and attitude toward preventive cardiology.

In this paper, the authors describe the development and validation of an inventory of preventive cardiology at the University of Virginia. The inventory contains two instruments designed to measure medical students' preinstructional and postinstructional knowledge of and attitude toward preventive cardiology. The knowledge test subscales provide unique and significant information about knowledge in preventive cardiology and can discriminate among groups differing in level of instruction and expertise in preventive cardiology. The attitude survey provides information about two attitude factors: cardiovascular disease prevention and cardiovascular disease research priorities. In the study reported here, attitudes appeared not to differ among groups of students with different preventive cardiology instructional levels and expertise. Both instruments were demonstrated to be useful measures of medical students' knowledge and attitudes concerning preventive cardiology educational programs.

Adult↗