Search PubMed⌕ Search

Biomedical subjects

A Burns

Publications and source records attributed to A Burns.

At least 217 records · Page 12Linked to original sources
PubMed1980

Redox and spectroscopic properties of oxidized MoFe protein from Azotobacter vinelandii.

The MoFe protein from Azotobacter vinelandii undergoes a six-electron oxidation by various organic dye oxidants with full retention of initial activity. Reduction of the oxidized protein by S2O42- and by controlled potential electrolysis indicates the presence of two reduction regions at -290 and -480 mV, each requiring three electrons for complete reaction. Control of the oxidation conditions provides a means for preparing two distinct MoFe protein species selectively oxidized by three electrons. Selective reduction of the redox region at -290 mV causes development of the EPR signal associated with fully reduced MoFe protein while reduction at -480 mV produces a change in the visible spectrum but has no effect on the EPR signal intensity. Kinetic differences for reduction of the two redox regions indicate that the cofactor region undergoes a more rapid reaction with reductant than the other metal redox sites.

Azotobacter↗
PubMed1977

Kinetics of dithionite ion utilization and ATP hydrolysis for reactions catalyzed by the nitrogenase complex from Azotobacter vinelandii.

The kinetics of S2O42-utilization and ATP hydrolysis during the nitrogenase-catalyzed H2 evolution and acetylene and nitrogen-reducing reactions were studied using a polarographic technique to monitor-S2O42-concentration. Rate constants for both S2O42-utilization and ATP hydrolysis were determined as a function of temperature and corresponding activation energies determined. The activation energy for ATP hydrolysis differs from that for product formation or S2O42-utilization by 5 kcal/mol above 20 degrees C and by 25 kcal/mol below 20 degrees C. The rate law for S2O42-utilization was determined and describes the enzyme catalyzed rate over a 1000-fold variation in S2O42-concentration and at least a 100-fold change in ATP concentration. The rate law for S2O42-utilization under N2-reducing conditions at 25 degrees C is given by -d([S2O42-]/dt = (2.3 x 10(-3) ET[S2O42-]1/2-[ATP]2)/([ATP]2 + K1[ATP] + K2), where ET is total enzyme concentration in mg/ml and K1 and K2 are equilibrium constants for ATP binding to nitrogenase. The half-order dependence of the rate on S2O42-concentration in interpreted in terms of the equilibrium S2O42- = 2SO2-, in which SO2- is the actual electron donor to nitrogenase. A partial mechanism incorporating these results is presented.

Acetobacter↗
PubMed1975

Stoichiometry, ATP/2e values, and energy requirements for reactions catalyzed by nitrogenase from Azotobacter vinelandii.

The stoichiometry of the nitrogenase ATP-dependent H2 evolution and ecetylene reduction reactions using S2O4(2-) as an electron source was studied by various techniques. For each mole of S2O4(2-) oxidized to 2SO3(2-) by the enzyme-catalyzed reactions at 25 degrees and pH 8, 1 mol of H2 (1 mol of ethylene for acetylene reduction) and two protons are produced. Under these conditions, 4.5 mol of ATP was hydrolyzed to ADP and inorganic phosphate for each S2O4(2-) oxidized. ATP/S2O4(2-) (ATP/2e) values determined at 5 degree intervals from 10 to 35 degrees were found to go through a minimum at 20 degrees. This effect is explained in terms of possible enzyme structure modifications. Calorimetric measurements for the enzyme-catalyzed H2 evolution and acetylene reduction reactions gave deltaH values of -32.4 and -75.1 kcal/mol of S2O4(2-), respectively.

Acetylene↗
PubMed1975

The thermochemical characterization of sodium dithionite, flavin mononucleotide, flavin-adenine dinucleotide and methyl and benzyl viologens as low-potential reductants for biological systems.

The heat of reaction (deltaH) of Fe(CN)63-, Methyl Viologen, FMN and FAD with S2O42- in aqueous buffer solutions was measured calorimetrically. In addition deltaH values for reduction of Fe(CN)63-, FMN and FAD by reduced Methyl Viologen were determined. The resulting calorimetric data and corresponding E0 values were combined to yield thermodynamic data for these simple reducing agents in a form useful for applications to biological reactions. Thermodynamic data for the reduction of spinach ferredoxin are also presented.

Calorimetry↗
PubMedDate not supplied

Self-assessment: a personalized approach to nursing during pregnancy.

A Prenatal Self-Assessment questionnaire was developed to aid in personalizing nursing care in a large medical center prenatal clinic. The questionnaire complements the standard prenatal record, which is intended primarily to document medical findings and treatment. The tool was used with more than 100 mothers who were receptive to this approach. The women's responses to questions about their feelings and thoughts concerning their pregnancies facilitated identification of potential problems and provided a basis for individualized and comprehensive care.

Consumer Behavior↗
PubMedDate not supplied

The effects of donepezil in Alzheimer's disease - results from a multinational trial.

Donepezil has been shown to be well tolerated and to improve cognition and global function in patients with mild to moderately severe Alzheimer's disease (AD). The current trial was undertaken to investigate further the efficacy and safety of donepezil, in a multinational setting, in patients with mild to moderately severe AD. This 30-week, placebo-controlled, parallel-group study consisted of a 24-week, double-blind treatment phase followed by a 6-week, single-blind, placebo washout. Eight hundred and eighteen patients with mild to moderately severe AD were randomly allocated to treatment with single, daily doses of 5 or 10 mg donepezil, or placebo. The two primary efficacy measures were: a cognitive performance test, the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) and a global evaluation, the Clinician's Interview-Based Impression of Change with caregiver input (CIBIC plus). Secondary outcome measures included the Sum of the Boxes of the Clinical Dementia Rating Scale (CDR-SB), a modified Interview for Deterioration in Daily living activities in Dementia (IDDD) and a patient rated quality of life assessment. Statistically significant improvements in cognitive and global function were observed, as evaluated by ADAS-cog and CIBIC plus, respectively, in both the 5 and 10 mg/day donepezil groups, compared with placebo. Treatment-associated changes were also observed in functional skills, as shown by improved scores on the CDR-SB and the complex-tasks component of the IDDD. A dose-response effect was evident, with the 10 mg/day donepezil group demonstrating greater benefits in all outcome measures than the 5 mg/day group. Donepezil was well tolerated by this patient population and did not produce any clinically significant laboratory test abnormalities. The results of this study confirm that donepezil is effective and well tolerated in treating the symptoms of mild to moderately severe AD.

Aged↗