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A Wallace

Publications and source records attributed to A Wallace.

At least 55 records · Page 3Linked to original sources
PubMed1996

Selection of potent inhibitors of farnesyl-protein transferase from a synthetic tetrapeptide combinatorial library.

Inhibitors of farnesyl-protein transferase (FPTase) show promise as anticancer agents. Based on the sequence of the protein substrates of FPTase (the CAAX sequence), potent and selective peptidomimetic inhibitors have been developed; these compounds share with the peptide substrate a free thiol and a C-terminal carboxylate. We have used a synthetic tetrapeptide combinatorial library to screen for new leads devoid of these features: the peptides were C-terminally amidated, and no free thiol was included in the combinatorial building blocks. To compensate for this negative bias, an expanded set of 68 amino acids was used, including both L and D as well as many non-coded residues. Sixteen individual tetrapeptides derived from the consensus were synthesized and tested; all were active, showing IC50 values ranging from low micromolar to low nanomolar. The most active peptide, D-tryptophan-D-methionine-D-4-chlorophenylalanine-L-gamma- carboxyglutamic acid (Ki = 2 nM), is also very selective showing little inhibitory activity against the related enzyme geranylgeranyl-protein transferase type I (IC50 > 50 microM). In contrast to CAAX-based peptidomimetics, D-tryptophan-D-methionine-D-4-chlorophenylalanine-L-gamma-carboxyglut amic acid appeared to mimic the isoprenoid substrate farnesyl diphosphate as determined by kinetic and physical measurements. D-Tryptophan-Dmethionine-D-4-chlorophenylalanine-L-gamma- carboxyglutamic acid was a competitive inhibitor of FPTase with respect to farnesyl diphosphate substrate and uncompetitive with respect to CAAX substrate. Furthermore, we demonstrated that FPTase undergoes ligand dependent conformational changes in its circular dichroism spectrum and that D-tryptophan-D-methionine-D-4-chlorophenylalanine-L-gamma- carboxyglutamic acid induced a conformational change identical to that observed with farnesyl diphosphate ligand.

Alkyl and Aryl Transferases↗
PubMed1996

Effect of atenolol on mortality and cardiovascular morbidity after noncardiac surgery. Multicenter Study of Perioperative Ischemia Research Group.

BACKGROUND: Perioperative myocardial ischemia is the single most important potentially reversible risk factor for mortality and cardiovascular complications after noncardiac surgery. Although more than 1 million patients have such complications annually, there is no effective preventive therapy. METHODS: We performed a randomized, double-blind, placebo-controlled trial to compare the effect of atenolol with that of a placebo on overall survival and cardiovascular morbidity in patients with or at risk for coronary artery disease who were undergoing noncardiac surgery. Atenolol was given intravenously before and immediately after surgery and orally thereafter for the duration of hospitalization. Patients were followed over the subsequent two years. RESULTS: A total of 200 patients were enrolled. Ninety-nine were assigned to the atenolol group, and 101 to the placebo group. One hundred ninety-four patients survived to be discharged from the hospital, and 192 of these were followed for two years. Overall mortality after discharge from the hospital was significantly lower among the atenolol-treated patients than among those who were given placebo over the six months following hospital discharge (0 vs. 8 percent, P<0.001), over the first year (3 percent vs. 14 percent, P=0.005), and over two years (10 percent vs. 21 percent, P=0.019). The principal effect was a reduction in deaths from cardiac causes during the first six to eight months. Combined cardiovascular outcomes were similarly reduced among the atenolol-treated patients; event-free survival throughout the two-year study period was 68 percent in the placebo group and 83 percent in the atenolol group (P=0.008). CONCLUSIONS: In patients who have or are at risk for coronary artery disease who must undergo noncardiac surgery, treatment with atenolol during hospitalization can reduce mortality and the incidence of cardiovascular complications for as long as two years after surgery.

Administration, Oral↗
PubMed1996

Use of a conformationally restricted secondary structural element to display peptide libraries: a two-stranded alpha-helical coiled-coil stabilized by lactam bridges.

A model for an alpha-helical peptide library based on a lactam bridged stabilized two-stranded alpha-helical coiled-coil is described. Sites for library display were incorporated in the middle of the peptide sequence of the most solvent accessible sites of a coiled-coil. A comparison was made between this coiled coil and a native coiled-coil based on the same sequence but lacking the lactam bridges. A lactam bridged peptide where the hydrophobic repeat consisted of all alanine residues, such that the tendency to dimerize would be diminished, was also prepared. This enabled us to determine the role tertiary interactions play in maintaining library positions in a helical conformation. The consensus sequence derived from a Zn finger library screened against an IgA reactive against the lipopolysaccharide of Shigella flexneri was transplanted into the peptides. CD spectroscopy revealed that although both coiled-coils are highly helical at 100 microM, the lactam bridge enhanced dimerization and allow the peptide to maintain its coiled-coil conformation at lower peptide concentrations. The helical content of the alanine based peptide was 69% and was independent of concentration over a range of 1.4 to 1410 microM. Urea denaturation studies indicated that the coiled-coils were considerably more stable than the alanine based peptide and that the lactam bridge coiled-coil was more stable than the native coiled coil by 1.6 kcal/mol. The lactam bridged coiled-coil was found to inhibit binding of the Zn finger peptide to the IgA in a concentration dependent manner with an IC50 of 5.0 microM whereas the peptide lacking the lactam bridges was much less effective in inhibiting binding. The alanine peptide was less active than the lactam bridged coiled-coil but more effective than the native coiled-coil with an IC50 of 16 microM. The versatility of the lactam stabilized coiled-coil template was demonstrated by incorporating five Gly residues into the library display sites. While the native coiled-coil adopted a random conformation the lactam bridged coiled-coil was 59% helical. Incorporation of a Cys-Gly-Gly linker to the N terminus and formation of a disulfide bond stabilized the peptide to the extent that it adopted a highly helical coiled-coil (94%) with a [urea]1/2 value of 5.9 M. Since the five glycine residues represent one of the most destabilizing combinations of amino acids that would be encountered at the five library display sites (with the exception of Pro), this stabilized coiled-coil should maintain its folded conformation regardless of the amino acids occupying the library positions.

Amino Acid Sequence↗
PubMed1996

Fluorescent multiplex microsatellites used to define haplotypes associated with 75 CFTR mutations from the UK on 437 CF chromosomes.

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene contains three highly informative microsatellites: IVS8CA, IVS17bTA, and IVS17bCA. Their analysis improves prenatal/ carrier diagnosis and generates haplotypes from CF chromosomes that are strongly associated with specific mutations. Microsatellite haplotypes were defined for 75 CFTR mutations carried on 437 CF chromosomes (220 for delta F508, 217 for other mutations) from Northern Ireland and three English regions: the North-West, East Anglia, and the South. Fluorescently labelled microsatellites were amplified in a triplex PCR reaction and typed using an ABI 373A fluorescent fragment analyser. These mutations cover all the common and most of the rare CF defects found in the UK, and their corresponding haplotypes and geographic region are tabulated here. Ancient mutations, delta F508, G542X, N1303K, were associated with several related haplotypes due to slippage during replication, whereas other common mutations were associated with the one respective haplotype (e.g., G551D and R560T with 16-7-17, R117H with 16-30-13, 621 + 1G > T with 21-31-13, 3659delC with 16-35-13). This simple, fast, and automated method for fluorescent typing of these haplotypes will help to direct mutation screening for uncharacterised CF chromosomes.

Chromosomes, Human↗
PubMed1996

Barriers to the use of urban medical services by rural and remote area households.

People from rural and remote areas commonly need to attend provincial and metropolitan cities for specialist care. There decisions to make such trips 'away' involve a number of non-medical considerations that include economic, emotional and social factors. This paper reports the results of two surveys that sought information about the types and importance of non-medical considerations taken into account by rural and remote Queensland householders when faced with a trip away. In addition, the problems encountered by respondents on their last trip away are reported and discussed. The data revealed that important considerations taken into account when planning the trip were predominantly related to urgency, household organisation and the costs likely to be incurred where away. A number of avoidable problems occurring at destination were also described. Generally, remote area respondents saw these impediments as more serious barriers to seeking care than did rural area respondents. When respondents were further asked to identify major problems associated with their last trip to an urban facility, problems at the destination figured more prominently, particularly problems directly related to the lack of understanding of the transport and distance needs of rural people. With one exception, these problems were reported by similar proportions of rural and remote area respondents. These are matters that merit high priority attention in any programs to enhance access to specialist medical services by people in rural and remote areas.

Emergencies↗
PubMed1996

Pilot study of the acceptability of cystic fibrosis carrier testing during routine antenatal consultations in general practice.

BACKGROUND: In 1989, the gene for cystic fibrosis was cloned and it became possible to detect carriers of the gene among the general population, including pregnant women. AIM: The aim of the pilot study was to assess the acceptability of integrating cystic fibrosis carrier testing into antenatal care by general practitioners at the first booking appointment. METHOD: Between 1 September 1991 and 31 August 1992, inclusive, all patients receiving routine antenatal care in a two-partner training practice in south Manchester were offered carrier testing for cystic fibrosis using a computer protocol for antenatal care developed by the practice. A questionnaire including a Spielberger state-trait anxiety inventory was sent to patients 2 weeks after they received the results of their carrier test, and interviews with the patients in their home were carried out 4 weeks and one year after they received the result. RESULTS: All but one patient (75 out of 76) booking before 14 weeks of pregnancy accepted the offer of cystic fibrosis carrier testing, and 96% (72 out of 75) felt that they had made the right decision and that they had enough time for discussion with their general practitioner before testing. CONCLUSIONS: Cystic fibrosis carrier testing can be successfully integrated into the antenatal booking appointment in general practice and is acceptable to patients. This is a model for other genetic screening opportunities resulting from advances in medical genetics.

Cystic Fibrosis↗
PubMed1995

A conformationally homogeneous combinatorial peptide library.

In search for a rational way to convert the information encoded in peptide structures into peptidomimetics, major progress could be made by coupling the power of selection methods, now enormously increased in number as a result of the development of combinatorial peptide libraries, with the rational design of structure-inducing templates for the selectable sequences. The availability of libraries of peptides with predetermined structure would enable selection-driven peptidomimetic design, whereby a conformational model for the peptide pharmacophore would be directly derived from the screening, allowing the design of a suitable non-peptidic scaffold to replace the peptide backbone. We describe here the first example of a conformationally homogeneous combinatorial peptide library, which yields ligands with the expected structure upon selection. The library was built by randomising five positions in the alpha-helical portion of a 26 amino acid Cys2His2 consensus "zinc-finger" motif. Since in zinc-fingers metal coordination and folding are coupled, in our library metal-dependent binding represents a built-in control against the selection of structurally undefined sequences. The alpha-helical library was produced as both fusion with the pVIII protein of filamentous phage and soluble peptides by chemical synthesis, the latter enabling the expansion of the selectable repertoire by the inclusion of non-coded amino acids. The two libraries were independently screened with the same receptor (a monoclonal IgA reactive against the lipopolysaccharide of the human pathogen Shigella flexneri), yielding a very similar consensus. In particular, the peptides defined by both methods showed very strong, zinc-dependent binding to the IgA. The geometrical arrangement of the side-chains of the selected peptide pharmacophore was shown by circular dichroism, Co(II)-complex absorption and high-resolution NMR to be structurally invariant with respect to the parent zinc-finger.

Amino Acid Sequence↗
PubMed1995

Lack of cross-reactivity of lytic antibodies with bloodstream forms of Trypanosoma cruzi zymodemes generated in a mouse experimental model.

Immune sera from mice infected with specific Zymodemes of Trypanosoma cruzi parasites displayed preferential in vitro complement-mediated trypanolytic activity with homologous or genetically related bloodstream trypomastigotes. Culture-derived and metacyclic trypomastigotes were more susceptible to lytic antibodies than bloodstream trypomastigote forms when the same serum panel was tested. Different levels of maximal trypanolytic reaction were observed when several parasites and sera were tested, suggesting that T. cruzi stocks are dissimilar in their efficiency to evade the lytic reaction, probably by capping and shedding mechanisms. A discussion based on the heterogeneity of surface antigens able to elicit the lytic response among different T. cruzi populations is presented.

Animals↗
PubMed1995

Distressed and nondistressed third- and sixth-grade children's self-reports of life events and impact and concordance with mothers.

This study examined the concordance of third- and sixth-grade distressed and nondistressed children's self-reports of the occurrence and perceived impact of life events that had occurred during the preceding 12 months with their mothers' perceptions. The study also examined whether maternal self-reports of dysphoria affects concordance between mother/child dyads on children's self-reports of occurrence and perceived impact of life events. Eighty-eight mother/child dyads, matched on Children's Depression Inventory scores, grade, sex, race, and school were included. Results indicated that distressed children endorsed more items on the Coddington Life Events Record (LER), and perceived them more negatively, than nondistressed children. Small, but statistically significant concordance rates were found between dyads on the occurrence of life events and the perceived impact of these events: Distressed children and their mothers had more mutually endorsed items than nondistressed children and mothers, and third-grade children had higher concordance rates with their mothers when compared to sixth-grade children. Third-grade children also appeared to commit more errors of commission on the LER. Finally, maternal distress mediated mother/child concordance. Possible explanations for these results and future research directions are discussed.

Child↗
PubMed1995

Replacing the glutamate ligand in the structural zinc site of Sulfolobus solfataricus alcohol dehydrogenase with a cysteine decreases thermostability.

The alcohol dehydrogenase gene from the thermophilic archaeum Sulfolobus solfataricus has been subcloned and expressed in Escherichia coli under the control of the T7 inducible promoter. The recombinant protein shows properties analogous to those of the native enzyme, including thermostability, despite the fact that E.coli does not post-translationally modify two lysine residues which are N-epsilon-methylated in the native enzyme. We constructed a 3-D model of the S.solfataricus alcohol dehydrogenase using the known structure of its isozyme from horse liver as a template. Our analysis of the structural zinc binding site suggested that this site is present and functional in the S.solfataricus enzyme and that a glutamate ligand can contribute to thermostability by influencing electrostatic interactions around the metal centre. To investigate this hypothesis, we constructed, expressed and characterized a mutant where the glutamate is replaced by a cysteine, thus restoring the zinc binding site of mesophilic alcohol dehydrogenases. The mutant shows the same activity but a reduced thermostability with respect to the wild-type recombinant protein, as suggested by our model.

Alcohol Dehydrogenase↗
PubMed1995

Linearity, load dependence, hysteresis, and clinical associations of systolic and diastolic indices of left ventricular function in man. Multicenter Study of Perioperative Ischemia (McSPI) Research Group.

Measures of left ventricular (LV) contractility must be linear, load-independent, free of hysteresis, and sensitive to changes in inotropic state. These properties of measures of LV contractility have been assessed previously in animals, but never in man. Using a micromanometer and volume conductance catheter technology, we measured LV pressure and volume in 67 patients scheduled for CABG surgery. Measurements of the maximum rate of change of pressure relative to time versus end-diastolic volume (dP/dtMax-EDV), preload recruitable stroke work (PLRSW) and the end-systolic pressure-volume relationship (ESPVR), and measurements of the maximum negative rate of change of pressure relative to time versus end-diastolic volume (-dP/dtMax-EDV) and the end-diastolic pressure-volume relationship (EDPVR) were obtained in 62 patients. Comparisons of these measures of contractility during preload reduction and augmentation were performed in 48 patients using paired and unpaired student's t-tests. Index linearity was determined using linear regression analysis. Neither the slope nor the intercept of any of the three measures of contractility changed significantly with loading conditions. Heart rate demonstrated no physiologically significant baroreceptor-mediated changes during the perturbations. Comparing measures of LV function--ejection fraction (EF%), LV end-diastolic pressure (LVEDP), dP/dtMax-EDV, PLRSW, ESPVR, -dP/dtMax-EDV, and end-diastolic pressure-volume relationship (EDPVR)--in patients with a preoperative medical history of congestive heart failure (CHF), myocardial infarction (MI), and hypertension (HTN) demonstrated lower EF percent (62.4 +/- 16.7 vs 42.8 +/- 5.0 [p < 0.0002]) and lower ESPVR (2.27 +/- 1.98 vs 1.30 +/- 0.83 [p < 0.03]) in patients with a history of CHF.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Disease↗
PubMed1995

Diagnostic issues in a family with late onset type 2 neurofibromatosis.

We report a family with type 2 neurofibromatosis and late onset tumours. Five members of this family have developed hearing loss late in life, two of whom have only been shown to have the diagnosis in their seventies, and three other obligate gene carriers died undiagnosed at 64, 72, and 78 years of age. A missense mutation at the C-terminal end of the NF2 protein has been identified in this family and segregates with disease. The use of highly polymorphic markers for predictive testing is also shown. There appears to be an autosomal dominant form of spinocerebellar degeneration which is segregating separately to NF2 in this family, which created a diagnostic dilemma.

Adolescent↗
PubMed1995

Characterization of monoclonal antibodies against Erwinia carotovora subsp. atroseptica serogroup I: specificity and epitope analysis.

The characteristics of two monoclonal antibodies (Mabs), A23/1221.59.44.d.3 (1221) and A23/1239.36.64.e.2 (1239), against Erwinia carotovora subsp. atroseptica serogroup I produced in this study were compared with those of two other independently obtained Mabs, 4G4 in Spain and 4F6 in Canada, using different strains as immunogen and different screening procedures. The reaction pattern of Mabs 1221 and 1239 determined by indirect ELISA on over 200 bacterial strains including five E.c. atroseptica and 36 E.c. carotovora serogroups, seven Erw. chrysanthemi biovars, 23 other plant bacterial pathogens and 33 saprophytic bacteria from potato was similar to that of 4G4. Specificity for E.c. atroseptica serogroup I was improved, especially when skimmed milk (Marvel) was used instead of bovine serum albumin as blocking agent. Mabs 1221, 1239 and 4G4 reacted positively with all 22 E.c. atroseptica serogroup I, the dominant E.c. atroseptica serogroup on potato, strains tested and only with two out of five E.c. atroseptica serogroup XXII strains, one E.c. carotovora serogroup XXI strain and one strain of a saprophytic bacterium, Comamonas sp. Essentially similar results were obtained when examined by immunofluorescence. Characterization of the four Mabs showed that they were IgG3 and SDS-PAGE/immunoblot results suggested that they were probably against the O-side chain of bacterial cell wall lipopolysaccharides. In competition ELISA between biotin-labelled and unlabelled Mabs, the competition pattern of the four Mabs was similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗