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Biomedical subjects

M A Noble

Publications and source records attributed to M A Noble.

At least 37 records · Page 2Linked to original sources
PubMed1997

A classical enzyme active center motif lacks catalytic competence until modulated electrostatically.

The cysteine proteinase superfamily is a source of natural structural variants of value in the investigation of mechanism. It has long been considered axiomatic that catalytic competence of these enzymes mirrors the generation of the ubiquitous catalytic site imidazolium-thiolate ion pair. We here report definitive evidence from kinetic studies supported by electrostatic potential calculations, however, that at least for some of these enzymes the ion pair state which provides the nucleophilic and acid-base chemistry is essentially fully developed at low pH where the enzymes are inactive. Catalytic competence requires an additional protonic dissociation with a common pKa value close to 4 possibly from the Glu50 cluster to control ion pair geometry. The pH dependence of the second-order rate constant (k) for the reactions of the catalytic site thiol groups with 4,4'-dipyrimidyl disulfide is shown to provide the pKa values for the formation and deprotonation of the (Cys)-S-/(His)-Im+H ion pair state. Analogous study of the reactions with 2,2'-dipyridyl disulfide reveals other kinetically influential ionizations, and all of these pKa values are compared with those observed in the pH dependence of kcat/Km for the catalyzed hydrolysis of N-acetylphenylalanylglycine 4-nitroanilide. The discrepancy between the pKa value for ion pair formation and the common pKa value close to 4 related to generation of catalytic activity is particularly marked for ficin (pKa 2.49 +/- 0.02) and caricain (pKa 2.88 +/- 0.02) but exists also for papain (pKa 3.32 +/- 0.01).

Binding Sites↗
PubMed1997

Effects of protein kinase C inhibitors in in situ and isolated ischemic rabbit myocardium.

We tested the effects of the protein kinase C (PKC) inhibitors bisindolylmaleimide (1 microM) and chelerythrine (2 microM) on myocardial ischemia-reperfusion injury in in situ and isolated perfused rabbit hearts. In non-ischemic isolated hearts, bisindolylmaleimide (1 microM) and chelerythrine (2 microM) blocked sn-1,2-dioctanoylglycerol (DOG)-induced coronary vasoconstriction by approximately 80%. Intact hearts were subjected to 45 min coronary artery occlusion and 2 h reperfusion. Infarct size, determined by triphenyltetrazolium chloride (TTC)-staining and expressed as percentage of risk area, was reduced approximately 50% by both bisindolylmaleimide (0.05 mg/kg, i.v.) and chelerythrine (0.1 mg/kg, i.v.) compared to vehicle treated controls. In contrast, a higher dose of chelerythrine (3.8 mg/kg, i.v.) did not significantly reduce infarct size. Isolated hearts were subjected to 45 min of global normothermic (37 degrees C) ischemia and 60 min reperfusion. Control hearts exhibited 45+/-2% recovery of pre-ischemic left ventricular developed pressure (LVDP) compared to bisindolylmaleimide- (73+/-7%) and chelerythrine-treated hearts (70+/-11%). Bisindolylmaleimide and cherythrine reduced infarct size from a control value of 24+/-4 to 8+/-2 and 9+/-3%, respectively. Preconditioning isolated hearts with 5 min ischemia and 10 min reperfusion prior to prolonged ischemia reduced infarct size to 10.4+/-2.3%, an effect which was blocked by chelerythrine (22.5+/-4.2% infarct size). These results suggest that although PKC may play a role in ischemic preconditioning, PKC inhibitors can be cardioprotective during prolonged ischemia.

Alkaloids↗
PubMed1995

Different effects of an adenosine A1 analogue and ischemic preconditioning in isolated rabbit hearts.

BACKGROUND: Ischemic preconditioning reduces infarct size, but its effects on postischemic function are variable. Adenosine, which is thought to play a role in ischemic preconditioning, reduces both infarct size and postischemic dysfunction. The purpose of this study was to compare the cardioprotective effects of ischemic preconditioning and an adenosine A1 receptor agonist on recovery of function and infarct size in isolated rabbit hearts. METHODS: Krebs buffer-perfused hearts (at least 7 per group) were subjected to 60 minutes of global ischemia (37 degrees C) and 60 minutes of reperfusion. Ventricular function was assessed by measuring left ventricular developed pressure, and infarct size (percentage of the left ventricle) was determined by tetrazolium staining. RESULTS: Control hearts exhibited 34% +/- 6% infarct size and 56% +/- 4% recovery of preischemic left ventricular developed pressure. Ischemic preconditioning reduced infarct size to 13% +/- 1% but had no effect on recovery of function (65% +/- 5%). Hearts treated with the adenosine A1 agonist R-phenylisopropyladenosine for 5 minutes immediately before ischemia exhibited both reduced infarct size (10% +/- 2%) and enhanced postischemic recovery of left ventricular developed pressure (86% +/- 3%). Termination of the R-phenylisopropyladenosine treatment before ischemia eliminated its beneficial effects. The adenosine A1 receptor antagonist DPCPX blocked both of the effects of R-phenylisopropyladenosine but did not block ischemic preconditioning. CONCLUSIONS: These results demonstrate fundamental differences between the cardioprotective effects of adenosine A1 receptor activation and ischemic preconditioning.

Animals↗
PubMed1995

Xanthomonas maltophilia misidentified as Pseudomonas cepacia in cultures of sputum from patients with cystic fibrosis: a diagnostic pitfall with major clinical implications.

Pseudomonas cepacia infection in patients with cystic fibrosis (CF) has major significance in terms of infection control, psychosocial issues, and medical treatment. We describe three instances in which the diagnostic laboratory misidentified Xanthomonas maltophilia as P. cepacia in cultures of sputum from patients with CF. These errors were recognized when 3 (9%) of 32 isolates, which had all been identified as P. cepacia and had been submitted to the Canadian Pseudomonas Repository Laboratory (Vancouver, BC), were correctly identified there as X. maltophilia. Each of the three isolates grew well on P. cepacia media, turned a characteristic vivid pink color, were polymyxin-resistant, and were lysine-positive. All three were initially characterized incorrectly as oxidase-positive and DNase-negative. The diagnostic laboratory then reexamined 24 other isolates that had been identified as P. cepacia; complete biochemical testing confirmed that all were indeed P. cepacia. Because infection due to P. cepacia has major implications for patients with CF, when a possible strain of P. cepacia is isolated, careful and complete characterization should be performed.

Adult↗
PubMed1995

The search for healing: is it possible in contemporary health care?

Several cases are presented in which the patient received less than optimum care and treatment from the current health care delivery system. Nursing interventions for these cases are proposed consistent with four nursing roles and functions that are necessary to make possible true healing. Patients must not feel that obtaining health care is like a business transaction. The real challenge for nursing in contemporary health care systems is to maintain a therapeutic relationship with patients.

Adult↗
PubMed1994

Adenosine attenuates phorbol ester-induced negative inotropic and vasoconstrictive effects in rat hearts.

Phorbol esters reduce cardiac contractility and produce coronary vasoconstriction presumably by stimulating protein kinase C (PKC). We tested whether adenosine altered the response to phorbol 12-myristate 13-acetate (PMA) in isolated rat hearts. Hearts, perfused at constant flow and constant heart rate, were exposed to PMA (10 nM) for 30 min and then allowed 30 min of recovery. PMA reduced left ventricular developed pressure (LVDP) from 81 +/- 2 to 49 +/- 3 and 40 +/- 2 mmHg (51 +/- 3% of baseline LVDP) after 30 min infusion and 30 min recovery, respectively. PMA also increased coronary perfusion pressure to 224 +/- 13% of baseline after 60 min. The PKC inhibitor bisindolylmaleimide (0.5 microM) blocked the PMA-induced negative inotropy and vasoconstriction. Adenosine (100 microM) and the A1-agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 0.1 microM) significantly attenuated the negative inotropic effect of PMA as LVDP was maintained at 81 +/- 4% and 99 +/- 7% of baseline, whereas CGS-21680, an A2-agonist, had no beneficial effect on function (54 +/- 4% of baseline). Adenosine and CGS-21680 (0.1 microM), but not CCPA, significantly attenuated PMA-induced coronary vasoconstriction. These results suggest that adenosine receptor activation may modulate myocardial PKC activity or attenuate the effects of increased PKC activity.

Adenosine↗
PubMed1993

Case-control and vector studies of nosocomial acquisition of Pseudomonas cepacia in adult patients with cystic fibrosis.

OBJECTIVE: To examine factors associated with nosocomial acquisition of Pseudomonas cepacia in adult patients with cystic fibrosis. DESIGN: A retrospective case-control study of 5 patients with nosocomial acquisition of P cepacia versus 20 matched controls who failed to develop P cepacia infection. Selective handwashing, air sampling, and respiratory equipment sampling also were performed. SETTING: A university hospital providing tertiary care to 95 adult cystic fibrosis patients. PATIENTS: All patients are adults with known cystic fibrosis. Case definition required multiple negative sputum cultures for P cepacia prior to and during admission, with a positive sputum culture prior to discharge. Controls had negative sputum cultures for P cepacia prior to and throughout hospitalization. Controls were matched for age, gender, disease severity, and frequency of hospitalizations. RESULTS: Factors associated with increased risk of nosocomial acquisition of P cepacia included receiving humidifier or nebulized treatments (60% versus 5%, p = .016, odds ratio = 28.5, 95% confidence interval = 1.93 to 420.58). Factors without significance included ward, room, teaching versus nonteaching status, use of steroids, sharing a hospital room with another cystic fibrosis patient, antibiotic use, presence of portocath in situ, or socializing with another individual with cystic fibrosis known to be P cepacia-positive. Air sampling studies failed to demonstrate aerosolization of P cepacia by coughing cystic fibrosis patients over a 1-hour sampling time. Handwashing studies failed to demonstrate P cepacia on hands of cystic fibrosis patients, nurses, or physiotherapists (before or after physiotherapy). Reservoirs from nebulizers consistently grew P cepacia following therapy. CONCLUSIONS: Respiratory equipment may be an important source of nosocomial acquisition of P cepacia in adult cystic fibrosis patients.

Adult↗
PubMed1993

Enzyme rate assay for 5-fluorocytosine.

Modification of an enzyme assay for 5-fluorocytosine, from an end point to a rate analysis, has resulted in a method that can provide results within 10 minutes. The modification also rendered the assay less susceptible to interference from bilirubin and triglycerides. This obviated the need to correct 5-fluorocytosine results for icteric or moderately lipemic samples. The performance history of the enzyme rate method has shown that it is reliable, quick, cost-effective, and suitable for use in a clinical laboratory.

Aminohydrolases↗
PubMed1993

Temperature-sensitive mutation in lytF, a new gene involved in autolysis of Escherichia coli.

A temperature-sensitive mutation in a new Escherichia coli gene, located at 62.5 min on the linkage map and designated lytF, resulted in bacteriolysis at the restrictive temperature. Temperature sensitivity and lytF-mediated lysis were simultaneously suppressed by either of two previously described unlinked mutations designated smhA1 and smhB1. The smhA1 and smhB1 alleles were originally isolated as specific extragenic suppressors of temperature-sensitive mutations in three other genes known as murH (99 min), lytD (13 min) and lytE (25 min) which conferred lysis phenotypes indistinguishable from that of the lytF mutation. The murH, lytD and lytE genes have been proposed to be related on the bases of phenotypic similarities and the specificities of their extragenic suppressors. It is now further proposed that lytF belongs to this group. The isolation of new alleles of smhA and smhB as extragenic suppressors of lytF further supports this proposal.

Alleles↗
PubMed1991

Hepatitis & HIV: prevalence of infection and changing attitudes toward infection control procedures in British Columbia.

Dental professionals attending the annual meeting of the College of Dental Surgeons of British Columbia in June 1990 were involved in a survey to assess the prevalence of infection with Hepatitis B, Hepatitis C and Human Immunodeficiency viruses, the acceptance of vaccination for protection against Hepatitis B virus, and the compliance with infection control guidelines. Participation was voluntary and anonymous and required completion of a questionnaire and donation of a blood sample. Four hundred one of 1,995 convention attendees participated. Fourteen were found to have markers of Hepatitis B infection; 13 had antibodies to both Hepatitis B surface antigen and Hepatitis B core antigen, and one was positive for Hepatitis B surface antigen. One individual had markers for both Hepatitis C and Hepatitis B viruses. None tested positive for antibody to Human Immunodeficiency virus. Vaccination against Hepatitis B virus was reported overall by 67 percent of the participants, but dentists and hygienists had a higher rate of vaccination (82 percent and 81 percent, respectively) when compared to dental assistants (41 percent; P less than .001). Acceptance of infection control procedures was high, with 92 percent of participants reporting use of gloves for all patients and 82 percent reporting use of masks and eye protection.

Attitude of Health Personnel↗