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L A Wallace

Publications and source records attributed to L A Wallace.

At least 19 recordsLinked to original sources
PubMed2006

Analysis of indoor particle size distributions in an occupied townhouse using positive matrix factorization.

UNLABELLED: From late 1999 to early March 2000, measurements of particle number (particles 0.01-20 microm in aerodynamic diameter) concentrations were made inside of a townhouse occupied by two non-smoking adults and located in Reston, VA (approximately 25 miles northwest of Washington, DC). The particle size measurements were made using an SMPS and an APS as well as a Climet optical scattering instrument. In this study, positive matrix factorization (PMF) was used to study the indoor particle size distributions. The size distributions or profiles obtained were identified by relating the obtained source contributions to the source information provided by the occupants. Nine particle sources were identified, including two sources associated with gas burner use: boiling water and frying tortillas. Boiling water for tea or coffee was found to be associated only with the smallest particles, with a number mode close to the detection limit of the SMPS (i.e., 0.01 microm). Frying tortillas produced particles with a number mode at about 0.09 microm while broiling fish produced particles with a number mode at about 0.05 microm. A citronella candle was often burned during the study period, and this practice was found to produce a 0.2-microm modal number distribution. Other indoor particle sources identified included sweeping/vacuuming (volume mode at 2 microm); use of the electric toaster oven (number mode at 0.03 microm); and pouring of kitty litter (volume mode over 10 microm). Two outdoor sources were also resolved: traffic (number mode at about 0.15 microm) and wood smoke (major number mode at about 0.07 microm). The volume distributions showed presence of coarse particles in most of the resolved indoor sources probably caused by personal cloud emissions as the residents performed the various indoor activities. PRACTICAL IMPLICATIONS: This study has shown that continuous measurements of indoor particle number and volume concentrations together with records of personal activities are useful for indoor source apportionment models. Each of the particle sources identified in this study produces distinct size distributions that may be useful in studying the mortality and morbidity effects of airborne particulate matter because they will have different penetrability and deposition patterns.

Air Pollution, Indoor↗
PubMed2005

Costs of running a universal adolescent hepatitis B vaccination programme.

In the first UK study to examine feasibility and acceptability of universal adolescent hepatitis B vaccination, the costs associated with the administration and uptake (80.2 and 89.3% for three doses and at least two doses, respectively), of a three-dose regimen in pupils in Glasgow schools (2001/2002) were measured. These data were used to estimate the economic outlay for the delivery of a routine, ongoing three-dose and two-dose hepatitis B vaccine programme in schools. Vaccine, accounting for almost 70% of the overall costs, was the largest cost item for both the pilot and routine programmes, using either regimen. However, the ongoing, two-dose regimen was the cheapest option in this analysis, irrespective of vaccine price. Cost data from this study may be useful for other countries wishing to implement a similar programme.

Adolescent↗
PubMed2004

Determinants of universal adolescent hepatitis B vaccine uptake.

The UK is currently considering the introduction of universal hepatitis B vaccination. This study of determinants of vaccine uptake among school based adolescents shows that living in areas of high deprivation, commonly associated with injecting drug risk behaviours, was the most important factor, with statistically significant lower odds of receiving three doses. This was less pronounced for receipt of two doses. Thus, there are implications for future policy; if universal vaccination is approved, a licensed two dose schedule would be most appropriate in this setting.

Adolescent↗
PubMed2002

Continuous measurements of air change rates in an occupied house for 1 year: the effect of temperature, wind, fans, and windows.

A year-long investigation of air change rates in an occupied house was undertaken to establish the effects of temperature, wind velocity, use of exhaust fans, and window-opening behavior. Air change rates were calculated by periodically injecting a tracer gas (SF(6)) into the return air duct and measuring the concentration in 10 indoor locations sequentially every minute by a gas chromatograph equipped with an electron capture detector. Temperatures were also measured outdoors and in the 10 indoor locations. Relative humidity (RH) was measured outdoors and in five indoor locations every 5 min. Wind speed and direction in the horizontal plane were measured using a portable meteorological station mounted on the rooftop. Use of the thermostat-controlled attic fan was recorded automatically. Indoor temperatures increased from 21 degrees C in winter to 27 degrees C in summer. Indoor RH increased from 20% to 70% in the same time period. Windows were open only a few percent of the time in winter but more than half the time in summer. About 4600 hour-long average air change rates were calculated from the measured tracer gas decay rates. The mean (SD) rate was 0.65 (0.56) h(-1). Tracer gas decay rates in different rooms were very similar, ranging only from 0.62 to 0.67 h(-1), suggesting that conditions were well mixed throughout the year. The strongest influence on air change rates was opening windows, which could increase the rate to as much as 2 h(-1) for extended periods, and up to 3 h(-1) for short periods of a few hours. The use of the attic fan also increased air change rates by amounts up to 1 h(-1). Use of the furnace fan had no effect on air change rates. Although a clear effect of indoor-outdoor temperature difference could be discerned, its magnitude was relatively small, with a very large temperature difference of 30 degrees C (54 degrees F) accounting for an increase in the air change rate of about 0.6 h(-1). Wind speed and direction were found to have very little influence on air change rates at this house.

Air Movements↗
PubMed2002

Universal hepatitis B vaccination of UK adolescents: a feasibility and acceptability study.

The feasibility of introducing universal hepatitis B immunisation was assessed by offering the vaccine to all 11-12 year old pupils in Greater Glasgow (approximately 10,800). Consent was received from 92% of the school roll, and 91.3%, 89.2% and 80.3% received at least 1, at least 2, and 3 doses respectively. The findings of this study constitute key evidence for the ongoing debate in the UK on hepatitis B vaccination.

Adolescent↗
PubMed2000

Equilibrium folding of dimeric class mu glutathione transferases involves a stable monomeric intermediate.

The conformational stabilities of two homodimeric class mu glutathione transferases (GSTM1-1 and GSTM2-2) were studied by urea- and guanidinium chloride-induced denaturation. Unfolding is reversible and structural changes were followed with far-ultraviolet circular dichroism, tryptophan fluorescence, enzyme activity, chemical cross-linking, and size-exclusion chromatography. Disruption of secondary structure occurs as a monophasic transition and is independent of protein concentration. Changes in tertiary structure occur as two transitions; the first is protein concentration dependent, while the second is weakly dependent (GSTM1-1) or independent (GSTM2-2). The second transition corresponds with the secondary structure transition. Loss in catalytic activity occurs as two transitions for GSTM1-1 and as one transition for GSTM2-2. These transitions are dependent upon protein concentration. The first deactivation transition coincides with the first tertiary structure transition. Dimer dissociation occurs prior to disruption of secondary structure. The data suggest that the equilibrium unfolding/refolding of the class mu glutathione transferases M1-1 and M2-2 proceed via a three-state process: N(2) <--> 2I <--> 2U. Although GSTM1-1 and GSTM2-2 are homologous (78% identity/94% homology), their N(2) tertiary structures are not identical. Dissociation of the GSTM1-1 dimer to structured monomers (I) occurs at lower denaturant concentrations than for GSTM2-2. The monomeric intermediate for GSTM1-1 is, however, more stable than the intermediate for GSTM2-2. The intermediates are catalytically inactive and display nativelike secondary structure. Guanidinium chloride-induced denaturation yields monomeric intermediates, which have a more loosely packed tertiary structure displaying enhanced solvent exposure of its tryptophans and enhanced ANS binding. The three-state model for the class mu enzymes is in contrast to the equilibrium two-state models previously proposed for representatives of classes alpha/pi/Sj26 GSTs. Class mu subunits appear to be intrinsically more stable than those of the other GST classes.

Anilino Naphthalenesulfonates↗
PubMed2000

Domain-domain interface packing at conserved Trp-20 in class alpha glutathione transferase impacts on protein stability.

The folding and assembly of the dimeric glutathione transferases (GST) involves the association of two structurally distinct domains per subunit. A prominent and conserved domain-domain interaction in class alpha GSTs is formed by the packing of the indole side chain of Trp-20 from domain I into a hydrophobic pocket in domain II. Stability studies have shown that partial dissociation of the domains near Trp-20 occurs as an initial fast event during the unfolding kinetics of human GSTA1-1 (Wallace et al., Biochemistry 37 (1998) 5320-5328; Wallace et al., Biochem. J. 336 (1998) 413-418). The contribution of Trp-20 toward stabilising the domain-domain interface was investigated by mutating it to either a phenylalanine (W20F) or alanine (W20A) and determining the functionality (catalysis and non-substrate ligand binding) and stability (thermal- and urea-induced denaturation) of the mutant proteins. The replacement of Trp-20 did not impact on the protein's gross structural properties. Functionally, the W20F was non-disruptive, whereas the cavity-creating W20A mutation was. Both mutants destabilised the native state with W20A exerting the greatest effect. Reduced m-values as well as the protein concentration dependence of the urea unfolding transitions for W20F GSTA1-1 suggest the presence of a dimeric intermediate at equilibrium that is not observed with wild-type protein. Unfolding kinetics monitored by stopped-flow tyrosine fluorescence was mono-exponential and corresponded to the global unfolding of the protein during which the dimeric intermediate unfolds to two unfolded monomers. The similar unfolding kinetics data for wild-type and W20F A1-1 indicates that the global unfolding event was not affected by amino acid replacement. We propose that the packing interactions at the conserved Trp-20 plays an important role in stabilising the intrasubunit domain I-domain II interface of class alpha GSTs.

Amino Acid Sequence↗
PubMed2000

The hydrophobic lock-and-key intersubunit motif of glutathione transferase A1-1: implications for catalysis, ligandin function and stability.

A hydrophobic lock-and-key intersubunit motif involving a phenylalanine is a major structural feature conserved at the dimer interface of classes alpha, mu and pi glutathione transferases. In order to determine the contribution of this subunit interaction towards the function and stability of human class alpha GSTA1-1, the interaction was truncated by replacing the phenylalanine 'key' Phe-51 with serine. The F51S mutant protein is dimeric with a native-like core structure indicating that Phe-51 is not essential for dimerization. The mutation impacts on catalytic and ligandin function suggesting that tertiary structural changes have occurred at/near the active and non-substrate ligand-binding sites. The active site appears to be disrupted mainly at the glutathione-binding region that is adjacent to the lock-and-key intersubunit motif. The F51S mutant displays enhanced exposure of hydrophobic surface and ligandin function. The lock-and-key motif stabilizes the quaternary structure of hGSTA1-1 at the dimer interface and the protein concentration dependence of stability indicates that the dissociation and unfolding processes of the mutant protein remain closely coupled.

Amino Acid Motifs↗
PubMed2000

Effects of influenza vaccination of health-care workers on mortality of elderly people in long-term care: a randomised controlled trial.

BACKGROUND: Vaccination of health-care workers has been claimed to prevent nosocomial influenza infection of elderly patients in long-term care. Data are, however, limited on this strategy. We aimed to find out whether vaccination of health-care workers lowers mortality and the frequency of virologically proven influenza in such patients. METHODS: In a parallel-group study, health-care workers in 20 long-term elderly-care hospitals (range 44-105 patients) were randomly offered or not offered influenza vaccine (cluster randomisation, stratified for policy for vaccination of patients and hospital size). All deaths among patients were recorded over 6 months in the winter of 1996-97. We selected a random sample of 50% of patients for virological surveillance for influenza, with combined nasal and throat swabs taken every 2 weeks during the epidemic period. Swabs were tested by tissue culture and PCR for influenza viruses A and B. FINDINGS: Influenza vaccine uptake in health-care workers was 50.9% in hospitals in which they were routinely offered vaccine, compared with 4.9% in those in which they were not. The uncorrected rate of mortality in patients was 102 (13.6%) of 749 in vaccine hospitals compared with 154 (22.4%) of 688 in no-vaccine hospitals (odds ratio 0.58 [95% CI 0.40-0.84], p=0.014). The two groups did not differ for proportions of patients positive for influenza infection (5.4% and 6.7%, respectively); at necropsy, PCR was positive in none of 17 patients from vaccine hospitals and six (20%) of 30 from no-vaccine hospitals (p=0.055). INTERPRETATION: Vaccination of health-care workers was associated with a substantial decrease in mortality among patients. However, virological surveillance showed no associated decrease in non-fatal influenza infection in patients.

Aged↗
PubMed2000

Reactivity of 13 in vitro expressed hepatitis B surface antigen variants in 7 commercial diagnostic assays.

The primary marker of current hepatitis B infection is the surface antigen (HBsAg), however HBsAg negativity does not exclude hepatitis B viremia. HBsAg variants can be responsible for such diagnostic failures. Here 13 different HBsAg variants were cloned, variant protein produced in a mammalian expression system, and tested using 7 commercial HBsAg diagnostic assays. Of 12 variants analyzed, 6 samples displayed similar reactivity to the positive control (containing standard HBsAg sequence) in most of the assays, but 6 samples, containing various mutations throughout the entire major hydrophilic region (MHR), showed reduced reactivity. It was found that the loss of cysteine at amino acid (aa) 124 in 1 sample affected the secretion as well as the reactivity of HBsAg in the expression system. Thus, not all assays are equally able to detect HBsAg variants, implying that, to attain an acceptable level of sensitivity, the antibody repertoire of the current assays should be extended.

Base Sequence↗
PubMed2000

Physiologically based pharmacokinetic modeling of the temperature-dependent dermal absorption of chloroform by humans following bath water exposures.

The kinetics of chloroform in the exhaled breath of human volunteers exposed skin-only via bath water (concentrations < 100 ppb) were analyzed using a physiologically based pharmacokinetic (PBPK) model. Significant increases in exhaled chloroform (and thus bioavailability) were observed as exposure temperatures were increased from 30 to 40 degrees C. The blood flows to the skin and effective skin permeability coefficients (Kp) were both varied to reflect the temperature-dependent changes in physiology and exhalation kinetics. At 40 degrees C, no differences were observed between males and females. Therefore, Kps were determined (approximately 0.06 cm/hr) at a skin blood flow rate of 18% of the cardiac output. At 30 and 35 degrees C, males exhaled more chloroform than females, resulting in lower effective Kps calculated for females. At these lower temperatures, the blood flow to the skin was also reduced. Total amounts of chloroform absorbed averaged 41.9 and 43.6 microg for males and 11.5 and 39.9 microg for females exposed at 35 and 40 degrees C, respectively. At 30 degrees C, only 2/5 males and 1/5 females had detectable concentrations of chloroform in their exhaled breath. For perspective, the total intake of chloroform would have ranged from 79-194 microg if the volunteers had consumed 2 liters of water orally at the concentrations used in this study. Thus, the relative contribution of dermal uptake of chloroform to the total body burdens associated with bathing for 30 min and drinking 2 liters of water (ignoring contributions from inhalation exposures) was predicted to range from 1 to 28%, depending on the temperature of the bath.

Adult↗
PubMed1999

Folding and assembly of dimeric human glutathione transferase A1-1.

Glutathione transferases function as detoxification enzymes and ligand-binding proteins for many hydrophobic endogenous and xenobiotic compounds. The molecular mechanism of folding of urea-denatured homodimeric human glutathione transferase A1-1 (hGSTA1-1) was investigated. The kinetics of change were investigated using far-UV CD, Trp20 fluorescence, fluorescence-detected ANS binding, acrylamide quenching of Trp20 fluorescence, and catalytic reactivation. The very early stages of refolding (millisecond time range) involve the formation of structured monomers with native-like secondary structure and exposed hydrophobic surfaces that have a high binding capacity for the amphipathic dye ANS. Dimerization of the monomeric intermediates was detected using Trp fluorescence and occurs as fast and intermediate events. The intermediate event was distinguished from the fast event because it is limited by a preceding slow trans-to-cis isomerization reaction (optically silent in this study). At high concentrations of hFKBP, dimerization is not limited by the isomerization reaction, and only the fast event was detected. The fast (tau = 200 ms) and intermediate (tau = 2.5 s) events show similar urea-, temperature-, and ionic strength-dependent properties. The dimeric intermediate has a partially functional active site ( approximately 20%). Final reorganization to form the native tertiary and quaternary structures occurs during a slow, unimolecular, urea- and ionic strength-independent event. During this slow event (tau = 250 s), structural rearrangements at the domain interface occur at/near Trp20 and result in burial of Trp20. The slow event results in the regain of the fully functional dimer. The role of the C-terminus helix 9 (residues 210-221) as a structural determinant for this final event is proposed.

Acrylamide↗
PubMed1999

Role of the C-terminal helix 9 in the stability and ligandin function of class alpha glutathione transferase A1-1.

Helix 9 at the C-terminus of class alpha glutathione transferase (GST) polypeptides is a unique structural feature in the GST superfamily. It plays an important structural role in the catalytic cycle. Its contribution toward protein stability/folding as well as the binding of nonsubstrate ligands was investigated by protein engineering, conformational stability, enzyme activity, and ligand-binding methods. The helix9 sequence displays an unfavorable propensity toward helix formation, but tertiary interactions between the amphipathic helix and the GST seem to contribute sufficient stability to populate the helix on the surface of the protein. The helix's stability is enhanced further by the binding of ligands at the active site. The order of ligand-induced stabilization increases from H-site occupation, to G-site occupation, to the simultaneous occupation of H- and G-sites. Ligand-induced stabilization of helix9 reduces solvent accessible hydrophobic surface by facilitating firmer packing at the hydrophobic interface between helix and GST. This stabilized form exhibits enhanced affinity for the binding of nonsubstrate ligands to ligandin sites (i.e., noncatalytic binding sites). Although helix9 contributes very little toward the global stability of hGSTA1-1, its conformational dynamics have significant implications for the protein's equilibrium unfolding/refolding pathway and unfolding kinetics. Considering the high concentration of reduced glutathione in human cells (about 10 mM), the physiological form of hGSTA1-1 is most likely the thiol-complexed protein with a stabilized helix9. The C-terminus region (including helix9) of the class alpha polypeptide appears not to have been optimized for stability but rather for catalytic and ligandin function.

Acrylamide↗
PubMed1999

Influenza diagnosis: from dark isolation into the molecular light. West of Scotland Respiratory Virus Study Group.

OBJECTIVES: To compare the conventional virus isolation method for diagnosis of influenza infection with reverse-transcription polymerase chain reaction (RT-PCR) in prospectively collected nose and throat swabs from elderly patients during the winter influenza season. The use of a denaturing buffer as an alternative to viral transport medium (VTM) for submission of combined nose and throat swabs to the laboratory for PCR was then investigated in a second study. METHODS: Virus was cultured in microtitre plates using two different cell lines and detected using monoclonal antibody staining. A multiplex, matrix gene PCR assay was optimized to increase the sensitivity and specificity of detection of influenza A (H3 and H1) and B nucleic acid. RESULTS: The multiplex assay detected all viruses with equal sensitivity to individual assays. In a large, multicentre field study PCR detected twice as many influenza infections compared with virus isolation. No positive culture was missed. PCR has a rapid turn around time (< 36 h) vs. a minimum of 7 days for virus isolation. Greater sensitivity and specificity in the PCR were achieved using a 'hot-start' method. Although the numbers were small, the detection rate using PCR was greater for swabs submitted in denaturing buffer than in VTM. CONCLUSIONS: PCR significantly increased the sensitivity and clinical utility of influenza A (H3 and H1) and B diagnosis. There were a number of advantages in using denaturing buffer for submission of samples, including high sensitivity, rapidity, ease of use and no requirement for the virus to be viable on arrival at the laboratory. Therefore, PCR is a rapid, sensitive and user-friendly alternative for influenza diagnosis. Virus isolation technology should be limited to referral centres for further epidemiological characterization.

Aged↗
PubMed1999

Antigenic characterization of pre- and post-liver transplant hepatitis B surface antigen sequences from patients treated with hepatitis B immune globulin.

BACKGROUND/AIMS: The success of treatment with hepatitis B hyperimmune globulin in preventing recurrence of hepatitis B virus infection in patients undergoing orthotopic liver transplantation depends on maintaining levels of anti-HBs sufficient to neutralise hepatitis B virus and also on patient compliance. Breakthrough infections may occur, and these have been associated with the emergence of variants in HBsAg. METHODS: Three patients, two who relapsed and one who had no evidence of hepatitis B virus infection post-orthotopic liver transplantation were studied. Polymerase chain reaction and sequencing of pre- and post-orthotopic liver transplantation samples was followed by antigenic analysis of the in vitro expressed cloned sequences. RESULTS: In two patients who were treated with hyperimmune globulin, amino acid variation in the region of the immunodominant B cell epitopes of HBsAg occurred. Sequencing of clones revealed fluctuating variant sequences over time. One had clinical relapse and immune escape was evident on in vitro antigenic analysis. Patient two lost HBsAg reactivity post-orthotopic liver transplantation. There was loss of an antigenically critical cysteine molecule; sequencing of clones revealed that this was the dominant species. The third patient relapsed when protective levels of anti-HBs were not maintained; HBsAg showed no variation compared to a standard subtype sequence. CONCLUSION: These data provide strong experimental evidence of immune escape. It appears that hyperimmune globulin provides the selection pressure. In these patients, HBsAg negativity does not exclude infection of the transplanted liver.

Aged↗
PubMed1998

A topologically conserved aliphatic residue in alpha-helix 6 stabilizes the hydrophobic core in domain II of glutathione transferases and is a structural determinant for the unfolding pathway.

A topologically conserved residue in alpha-helix 6 of domain II of human glutathione transferase (hGST) A1-1 was mutated to investigate its contribution to protein stability and the unfolding pathway. The replacement of Leu-164 with alanine (L164A) did not impact on the functional and gross structural properties of native hGST A1-1. The wild-type protein unfolds via a three-state pathway in which only folded dimer and unfolded monomer were highly populated at equilibrium; a native-like dimeric intermediate with partially dissociated domains I and II was detected using stopped-flow fluorescence studies [Wallace, Sluis-Cremer and Dirr (1998) Biochemistry 37, 5320-5328]. In the present study, urea-induced equilibrium unfolding of L164A hGST A1-1 indicated a destabilization of the native state and suggested the presence of a stable dimeric intermediate. The unfolding kinetic pathway for L164A hGST A1-1, like that for the wild type, is biphasic, with a fast and a slow unfolding event; the cavity-forming mutation has a substantially greater effect on the rate of unfolding of the fast event. The equilibrium and kinetic unfolding data for L164A hGST A1-1 suggest that a rapid pre-equilibrium is established between the native dimer and a dimeric intermediate before complete domain and subunit dissociation and unfolding. It is proposed that the topologically conserved bulky residue in alpha-helix 6 plays a role in specifying and stabilizing the core of domain II and the interface of domains I and II.

Amino Acid Sequence↗
PubMed1998

Equilibrium and kinetic unfolding properties of dimeric human glutathione transferase A1-1.

The equilibrium and kinetic unfolding properties of homodimeric class alpha glutathione transferase (hGST A1-1) were characterized. Urea-induced equilibrium unfolding data were consistent with a folded dimer/unfolded monomer transition. Unfolding kinetics were investigated, using stopped-flow fluorescence, as a function of denaturant concentration (3.5-8.9 M urea) and temperature (10-40 degrees C). The unfolding pathway, monitored by tryptophan fluorescence, was biphasic with a fast unfolding event (millisecond time range with enhanced fluorescence properties) and a slow unfolding event (seconds to minutes time range with quenched fluorescence properties). Both events occurred simultaneously from 3.5 M urea. Each phase displayed single-exponential behavior, consistent with two unimolecular reactions. Urea-dependence studies and thermodynamic activation parameters (transition-state theory) suggest that the transition state for each phase is well-structured and is closely related to native protein in terms of solvent exposure. The apparent activation Gibbs free energy change in the absence of denaturant, DeltaG (H2O), indicates that the slow unfolding event represents the transition state for the overall unfolding pathway. The rate and urea independence of each phase on the initial condition exclude the possibility of a preexisting equilibrium between various native forms in the pretransition baseline. The unfolding pathways monitored by energy transfer to or direct excitation of AEDANS covalently linked to Cys111 in hGST A1-1 were monophasic with urea and temperature properties similar to those observed for the slow unfolding event (described above). A sequential unfolding kinetic mechanism involving the partial dissociation of the two structurally distinct domains per subunit followed by complete domain and subunit unfolding is proposed.

Dimerization↗