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Biomedical subjects

A Berry

Publications and source records attributed to A Berry.

At least 91 records · Page 5Linked to original sources
PubMed1995

Altering kinetic mechanism and enzyme stability by mutagenesis of the dimer interface of glutathione reductase.

In wild-type glutathione reductase from Escherichia coli residues Val421 and Ala422 are located in an alpha-helix in a densely packed and hydrophobic region of the dimer interface, with their side chains packed against those of residues Ala422' and Val421' in the second subunit. A series of mutant glutathione reductases was constructed in which the identities of the residues at positions 421 and 422 were changed. Mutations were designed so as to present like charges (mutants Val421-->Glu:Ala422-->Glu and Val421-->Lys:Ala422-->Lys) or opposite charges (mutant Val421-->Lys:Ala422-->Glu) across the dimer interface to assess the role of electrostatic interactions in dimer stability. A fourth mutant (Val421-->His:Ala422-->His) was also constructed to investigate the effects of introducing a potentially protonatable bulky side chain into a crowded region of the dimer interface. In all cases, an active dimeric enzyme was found to be assembled but each mutant protein was thermally destabilized. A detailed steady-state kinetic analysis indicated that each mutant enzyme no longer displayed the Ping Pong kinetic behaviour associated with the wild-type enzyme but exhibited what was best described as a random bireactant ternary complex mechanism. This leads, depending on the chosen substrate concentration, to apparent sigmoidal, hyperbolic or complex kinetic behaviour. These experiments, together with others reported previously, indicate that simple mutagenic changes in regions distant from the active site can lead to dramatic switches in steady-state kinetic mechanism.

Alanine↗
PubMed1995

A reactive, surface cysteine residue of the class-II fructose-1,6-bisphosphate aldolase of Escherichia coli revealed by electrospray ionisation mass spectrometry.

The state of post-translational modification of the class-II fructose-1,6-bisphosphate aldolase (FBP-aldolase) purified from Escherichia coli was examined by electrospray ionisation mass spectrometry (ESI-MS). The mass was larger than that expected from the known DNA sequence by approximately 80 +/- 6 Da, suggesting the presence of a covalent modification on the protein. Phosphorylation (+ 80 Da), a known modification in an FBP-aldolase from Bacillus subtilis and a suspected modification in this E. coli aldolase, was ruled out as the extra mass was readily removed by treatment with dithiothreitol. Purification of aldolase by a protocol which omitted 2-mercaptoethanol from all buffers resulted in the purified protein having the expected mass (39016 Da). The extra mass was therefore established as a covalent adduct of the protein with 2-mercaptoethanol (+ 76 Da). Reduction and alkylation studies, followed by isolation of tryptic peptides, established that the site of attachment was Cys36. Although no significant effect of the modification on the activity of the protein was observed, the study underlines the ease with which a protein can be modified covalently by a simple and mild purification procedure; such labelling, which may not always be benign, would be undetectable without the routine use of mass spectrometric analysis.

Amino Acid Sequence↗
PubMed1995

The incidence of aspiration associated with the laryngeal mask airway: a meta-analysis of published literature.

STUDY OBJECTIVE: To determine the incidence of pulmonary aspiration with the laryngeal mask airway (LMA). DESIGN: A meta-analysis of all published literature on the LMA to September 1993. MEASUREMENTS AND MAIN RESULTS: All 547 publications were reviewed and coded, and those observational studies in which the LMA was the main form of airway management were analyzed. Pulmonary aspiration was defined as either the presence of bilious secretions or particulate matter in the tracheobronchial tree or, if bronchoscopy was not performed, a postoperative chest radiograph with infiltrates present on preoperative chest radiograph of physical examination. In the study population, there were 3 cases of aspiration in 12,901 patients, and when combined with four independent reports excluded from the detailed analysis, this gave a final incidence of 2 in 10,000. Ten confirmed pulmonary aspiration events from published case reports showed that most cases had one or more predisposing factors. No death of permanent disability occurred. CONCLUSIONS: The evidence to date suggests that the pulmonary aspiration with the LMA is uncommon and comparable to that for outpatient anesthesia with the face mask and tracheal tube. Meticulous attention to selection of low-risk patients and appropriate operative procedures and avoidance of light anesthesia should reduce the incidence even further.

Adolescent↗
PubMed1995

Physician supply and distribution in the USA.

The rising cost of US health care has precipitated some close examination as to the supply, distribution, and specialty choice of the physician workforce. It is an issue of considerable concern as America struggles to control health-care expenditures by shifting resources away from specialty medicine. Central to this problem are the various programmes and incentives which have encouraged an excess number of residency positions and specialty training. Examines the consequences of an unregulated medical school structure and provides an overview of current policy alternatives designed to increase the number of primary care physicians, correct the problems of physician maldistribution, and limit the overall number of medical school graduates.

Career Choice↗
PubMed1995

The laryngeal mask airway for dental surgery--a review.

The ideal airway requirements for oral surgery are the provision of a stable, unobstructed airway, protection of the lungs from aspiration, minimal interference with the surgical field and a low complication rate. Neither the nasal mask nor endotracheal tube meet these requirements. The laryngeal mask airway (LMA), provides a third type of airway for consideration in oral surgery that offers some of the benefits of intubation and avoids many of the associated hazards. It can be inserted without use of a laryngoscope or muscle relaxants, and is designed to produce an airtight seal around the laryngeal inlet. It provides a secure airway suitable for spontaneous or controlled ventilation and acts as an airtight throat pack. Scavenging of waste gases is possible, and it is well tolerated during recovery. A modification, specifically designed for head, neck and dental anaesthesia, has recently become available. The purpose of this article is to provide a brief overview of the LMA with special emphasis on its use in oral surgery.

Anesthesia, Dental↗
PubMed1995

Visit to suit the client not the system. Obtaining clients' views on district nurse visiting times.

1. Research, as well as personal experience, shows that clients and carers frequently find the visiting times of district nurses and other professionals inappropriate. 2. The study aimed to discover when clients/carers would prefer to schedule a district nurse's visit. 3. A questionnaire may not be a satisfactory method of critically appraising a district nursing service.

Community Health Nursing↗
PubMed1994

Reductive and oxidative half-reactions of glutathione reductase from Escherichia coli.

Glutathione reductase catalyzes the reduction of glutathione disulfide by NADPH and has a redox active disulfide and an FAD cofactor in each monomer. In the reductive half-reaction, FAD is reduced by NADPH and electrons pass from the reduced flavin to the redox active disulfide. The oxidative half-reaction is dithiol-disulfide interchange between the enzyme dithiol and glutathione disulfide. We have investigated the reductive and oxidative half-reactions using wild-type glutathione reductase from Escherichia coli and in an altered form of the enzyme in which the active site acid-base catalyst, His439, has been changed to an alanine residue (H439A). H439A has 0.3% activity in the NADPH/GSSG assay. The replacement affects both the oxidative half-reaction, as expected, and the reductive half-reaction--specifically, the passage of electrons from reduced flavin to the disulfide. Reduction of H439A by NADPH allows direct observation of flavin reduction. The NADPH-FAD charge transfer complex is formed in the dead time. Reduction of FAD, at a limiting rate of 250 s-1, is observed as a decrease at 460 nm and an increase at 670 nm (FADH(-)-NADP+ charge transfer). Subsequent passage of electrons from FADH- to the disulfide (increase at 460 nm and a decrease at 670 nm) is very slow (6-7 s-1) and concentration independent in H439A. The monophasic oxidative half-reaction is very slow, as expected for reduced H439A.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1994

A designed mutant of the enzyme glutathione reductase shortens the crystallization time by a factor of forty.

The packing of glutathione reductase from Escherichia coli in crystal form T showed a place where two molecules are at a distance of only 6 A between the closest atoms, i.e. where a contact is almost made. In order to form this contact with hydrogen bonds, two amino-acid residues were exchanged. This mutation had no effect on molecular packing or the resolution limit of the X-ray diffraction, but facilitated crystal nucleation dramatically and possibly increased the crystal growth rate and shortened the crystallization time.

Journal Article↗
PubMed1994

Didanosine compared with continuation of zidovudine in HIV-infected patients with signs of clinical deterioration while receiving zidovudine. A randomized, double-blind clinical trial. The Bristol-Myers Squibb AI454-010 Study Group.

OBJECTIVE: To determine the benefits of switching to didanosine compared with continuing zidovudine among patients infected with human immunodeficiency virus (HIV) who have previously used zidovudine and have signs of clinical deterioration. DESIGN: Randomized, double-blind, two-armed, parallel, comparative clinical trial with a blinded, compassionate crossover provision at 12 weeks. SETTING: Outpatient clinics at 19 tertiary care medical centers. PATIENTS: 312 patients infected with HIV who had received zidovudine for 6 months or more, had CD4 cell counts of 300/mm3 or less, and had signs of clinical deterioration within 12 weeks before study entry. INTERVENTION: Peroral didanosine tablets (600 mg/d adjusted for weight, "high dose") or zidovudine capsules (600 mg/d). MEASUREMENTS: Primary study end points were death, a new acquired immunodeficiency syndrome (AIDS)--defining event, or the combination of two new or recurrent HIV-related diagnoses with a 50% decrease in CD4 cells. RESULTS: Switching to didanosine was associated with fewer end points than continuing zidovudine (relative risk [RR] for zidovudine:didanosine = 1.5; 95% Cl, 1.1 to 2.0). This benefit was consistent across subgroups of patients with either AIDS-related complex or AIDS and was most apparent among those with a CD4 count at entry of 100/mm3 or more (RR = 2.2; Cl, 1.1 to 4.4). CONCLUSIONS: This study shows a positive treatment effect for switching from zidovudine to didanosine among patients with either AIDS-related complex or AIDS and validates the common practice of using clinical signs or a decrease in the CD4 count as an indication for changing therapy.

AIDS-Related Complex↗
PubMed1994

Anatomy of an engineered NAD-binding site.

The coenzyme specificity of Escherichia coli glutathione reductase was switched from NADP to NAD by modifying the environment of the 2'-phosphate binding site through a set of point mutations: A179G, A183G, V197E, R198M, K199F, H200D, and R204P (Scrutton NS, Berry A, Perham RN, 1990, Nature 343:38-43). In order to analyze the structural changes involved, we have determined 4 high-resolution crystal structures, i.e., the structures of the wild-type enzyme (1.86 A resolution, R-factor of 16.8%), of the wild-type enzyme ligated with NADP (2.0 A, 20.8%), of the NAD-dependent mutant (1.74 A, 16.8%), and of the NAD-dependent mutant ligated with NAD (2.2 A, 16.9%). A comparison of these structures reveals subtle differences that explain details of the specificity change. In particular, a peptide rotation occurs close to the adenosine ribose, with a concomitant change of the ribose pucker. The mutations cause a contraction of the local chain fold. Furthermore, the engineered NAD-binding site assumes a less rigid structure than the NADP site of the wild-type enzyme. A superposition of the ligated structures shows a displacement of NAD versus NADP such that the electron pathway from the nicotinamide ring to FAD is elongated, which may explain the lower catalytic efficiency of the mutant. Because the nicotinamide is as much as 15 A from the sites of the mutations, this observation reminds us that mutations may have important long-range consequences that are difficult to anticipate.

Binding Sites↗
PubMed1994

A quantitative methodology for the de novo design of proteins.

We have developed a general quantitative methodology for designing proteins de novo, which automatically produces sequences for any given plausible protein structure. The method incorporates statistical information, a theoretical description of protein structure, and motifs described in the literature. A model system embodying a portion of the quantitative methodology has been used to design many protein sequences for the phage 434 Cro and fibronectin type III domain folds, as well as several other structures. Residue sequences selected by this prototype share no significant identity with any natural protein. Nonetheless, 3-dimensional models of the designed sequences appear generally plausible. When examined using secondary structure prediction methods and profile analysis, the designed sequences generally score considerably better than the natural ones. The designed sequences are also in reasonable agreement with a sequence template. This quantitative methodology is likely to be capable of successfully designing new proteins and yielding fundamental insights about the determinants of protein structure.

Amino Acid Sequence↗
PubMed1994

Laryngeal mask airway cuff pressure and position during anaesthesia lasting one to two hours.

The cuff of the laryngeal mask airway (LMA) is highly permeable to nitrous oxide (N2O), and cuff pressure increases during N2O/O2 anaesthesia. The extent of these changes and their effect on LMA position have previously only been investigated for short procedures. The current study was designed to investigate the effects of nitrous oxide-oxygen (N2O/O2) anaesthesia lasting one to two hours on cuff pressure, LMA positioning and pharyngeal morbidity. Twenty-four male patients underwent spontaneous ventilation anaesthesia with 66% N2O in oxygen and isoflurane. Following insertion and inflation of a #4 LMA with 30 ml air, mean (SD) cuff pressures immediately increased from 107 (9) to 145 (12) mmHg and then at a decreasing rate for 90 min to peak at 215 (12) mmHg. There was a correlation between N2O concentration and final cuff volume (P < 0.001). There was no displacement of the LMA cuff in any patient. Three of 19 patients had a mild sore throat. This study demonstrates that the increase in LMA cuff pressure is self limiting over a one-to-two-hour period and does not cause displacement of the LMA. There is no evidence that cuff pressure monitoring and pressure limitation is necessary during LMA anaesthesia.

Adolescent↗