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Biomedical subjects

R M Burke

Publications and source records attributed to R M Burke.

9 recordsLinked to original sources
PubMed2002

Laccases and other polyphenol oxidases in ecto- and ericoid mycorrhizal fungi.

Polyphenol oxidases are known to be produced by a range of ectomycorrhizal (ECM) and ericoid mycorrhizal fungi. These enzymes include laccase (EC 1.10.3.2), catechol oxidase (EC 1.10.3.1) and tyrosinase (EC 1.14.18.1), between which there exists considerable overlap in substrate affinities. In this review we consider the nature and function of these enzymes, along with the difficulties associated with assigning precise enzymatic descriptions. The evidence for production of laccase and other polyphenol oxidases by ECM and ericoid mycorrhizal fungi is critically assessed and their potential significance to the mycorrhizal symbioses discussed.

Ascomycota↗
PubMed2002

The number of amino acid residues mismatches correlates with flow cytometry crossmatching results in high PRA renal patients.

Highly sensitized renal transplant candidates present a group at high risk for acute and chronic rejection. The probability of finding compatible donors for these recipients is significantly lower in comparison to those who have low PRA values. As a consequence, these patients spend longer time on the waiting list and become tethered to dialysis. The results of final cross match (XM) are critical for making a decision about whether such a candidate receives an organ or not. The degree of donor and recipient HLA compatibility predicts the results of XM. The goal of this study was to expand a variety of acceptable HLA-AB mismatches (MM) for high PRA kidney recipients using the HLAMATCHMAKER algorithm. This strategy focuses on the fine structural features of HLA polymorphism comprising amino acid residues or triplets (AAT), which are located in alpha-helical coils of HLA molecules and are available to antibodies. We analyzed serum samples from thirty-nine highly alloimmunized recipients (PRA > or = 85%). The level of sensitization was detected using FlowPRA Class I Screening Test. This group of transplant candidates included thirteen recipients who demonstrated negative results of final T/B FCXM and twenty-six, who were FCXM positive. The application of the HLAMATCHMAKER algorithm based on the HLA class I donor and recipient typing allowed us to detect the total number of AATMM as well as the number of immunogenic AAT in both FCXM negative and FCXM positive groups of recipients. Significantly greater numbers of both total and highly immunogenic AATMM have been emerged in the group of FCXM positive patients. Furthermore, the results of this analysis have shown a high degree of probability of positive FCXM if the number of highly immunogenic AATMM was > or = 1 (chi(2) = 22.9 Yate's correction; p = 0.000001). We did not observe overlapping between antibody specificity and permissible HLA-AB MM detected using the HLAMATCHMAKER strategy. Thus, the number of highly immunogenic AATMM can serve as a reliable predictive value for final FCXM results in highly sensitized renal transplant candidates. The HLAMATCHMAKER algorithm appears to be the proper strategy to find donors for high PRA recipients.

Adolescent↗
PubMed2002

Inhibition of toxicity and protofibril formation in the amyloid-beta peptide beta(25-35) using N-methylated derivatives.

Beta (25-35) is a fragment of beta-amyloid that retains its wild-type properties. N-methylated derivatives of beta(25-35) can block hydrogen bonding on the outer edge of the assembling amyloid, so preventing the aggregation and inhibiting the toxicity of the wild-type peptide. The effects are assayed by Congo Red and thioflavin T binding, electron microscopy and an MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] toxicity assay. N-methyl-Gly-25 has similar properties to the wild- type, while five other methylation sites have varying effects on prefolded fibrils and fibril assembly. In particular, N-methyl-Gly-33 is able to completely prevent fibril assembly and reduces the toxicity of prefolded amyloid. With N-methyl-Leu-34 the fibril morphology is altered and toxicity reduced. A preliminary study of beta(25-35) structure in aqueous solution was made by small-angle neutron scattering (SANS). The protofibrillar aggregates are best described as a disc of radius 140 A and height 53 A (1 A = 0.1 nm), though the possibility of polydisperse aggregates cannot be ruled out. No aggregates form in the presence of N-methyl-Gly-33. We suggest that the use of N-methylated derivatives of amyloidogenic peptides and proteins could provide a general solution to the problem of amyloid deposition and toxicity and that SANS is an important technique for the direct observation of protofibril formation and destruction in solution.

Alzheimer Disease↗
PubMed2000

Inhibition of toxicity in the beta-amyloid peptide fragment beta -(25-35) using N-methylated derivatives: a general strategy to prevent amyloid formation.

beta-(25-35) is a synthetic derivative of beta-amyloid, the peptide that is believed to cause Alzheimer's disease. As it is highly toxic and forms fibrillar aggregates typical of beta-amyloid, it is suitable as a model for testing inhibitors of aggregation and toxicity. We demonstrate that N-methylated derivatives of beta-(25-35), which in isolation are soluble and non-toxic, can prevent the aggregation and inhibit the resulting toxicity of the wild type peptide. N-Methylation can block hydrogen bonding on the outer edge of the assembling amyloid. The peptides are assayed by Congo red and thioflavin T binding, electron microscopy, and a 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) toxicity assay on PC12 cells. One peptide (Gly(25) N-methylated) has properties similar to the wild type, whereas five have varying effects on prefolded fibrils and fibril assembly. In particular, beta-(25-35) with Gly(33) N-methylated is able to completely prevent fibril assembly and to reduce the toxicity of prefolded amyloid. With Leu(34) N-methylated, the fibril morphology is altered and the toxicity reduced. We suggest that the use of N-methylated derivatives of amyloidogenic peptides and proteins could provide a general solution to the problem of amyloid deposition and toxicity.

Amyloid beta-Peptides↗
PubMed1997

Characterisation of equine matrix metalloproteinase 2 and 9; and identification of the cellular sources of these enzymes in joints.

The cellular production by resident articular cells and infiltrating inflammatory cells of the gelatinase matrix metalloproteinases (MMP) was investigated by tissue culture methods and analysis of cell supernatants by gelatin zymography. Peripheral blood neutrophils in short term culture produced MMP-9, as did peripheral blood monocytes in culture. Isolated articular chondrocytes in monolayer culture produced both MMP-2 and MMP-9, although articular cartilage maintained as explant culture produced MMP-2 alone. Synovial fibroblasts grown in monolayer culture produced MMP-2 alone, although synovial membrane in explant culture produced both MMP-2 and the active form of MMP-2. Lysis of blood polymorph neutrophils produced large quantities of MMP-9, but lysis of blood monocytes, synovial fibroblasts and articular chondrocytes produced little enzyme indicating that, unlike the other cell types, polymorph neutrophils store MMPs intracellularly. Equine MMP-2 was purified from synovial fibroblast cell culture supernatant, and equine MMP-9 from polymorph neutrophil cell culture supernatant, by gelatin-sepharose affinity chromatography. The 2 enzymes were identified from their molecular weights and by their respective N-terminal amino acid sequences which showed homology with the enzymes from other species. The demonstration that invasive cells and resident articular cells can produce enzymes which are capable of digestion of certain component molecules of the articular cartilage matrix, shows that therapeutic targeting of these enzymes could be a valid proposition in the prevention of cartilage destruction in osteoarthritis.

Amino Acid Sequence↗
PubMed1992

Reversible late potentials due to ischemia.

The role of ischemia in the development of reversible late potentials was assessed in 19 patients undergoing percutaneous transluminal coronary angioplasty. Signal-averaged electrocardiograms were performed before angioplasty, during ischemia caused by balloon inflation and after angioplasty. Five of 19 patients developed late potentials that reverted to normal after angioplasty. Age, sex, ejection fraction, left ventricular end diastolic pressure, vessels involved, and extent of myocardium in jeopardy did not predict the development of late potentials. Patients with a prior history of myocardial infarction were more likely to develop late potentials. Therefore, patients with prior myocardial infarction appear more likely to develop the substrate for reentrant ventricular tachycardia during periods of ischemia.

Angioplasty, Balloon, Coronary↗
PubMed1990

Growth of Bacillus stearothermophilus on glycerol in chemostat culture: expression of an unusual phenotype.

Bacillus stearothermophilus grew readily on glycerol in carbon-limited chemostat culture and expressed a high carbon conversion efficiency. However, the strain of organism used (probably B. stearothermophilus var. nondiastaticus) proved particularly sensitive to glycerol, both respiration and growth being severely impeded by any surfeit of this compound. Sensitivity was found to correlate with an exceptionally high level of expression of glycerol kinase [activities of more than 80 mumol min-1 (mg protein)-1 were manifest in crude cell-free extracts], coupled with low activities of methylglyoxal synthase and of glyoxylase (enzymes of the methylglyoxal bypass). It is proposed that metabolic dysfunction results from an uncontrolled gross accumulation of glycerol phosphate (and early products of its metabolism) within the cells, coupled with depletion of the intracellular phosphate pool.

Carbon Dioxide↗
PubMed1979

The Ottawa County project: a report of a tuberculosis screening project in a small mining community.

Following a retrospective review of tuberculosis cases reported from Ottawa County, Oklahoma, from 1969 through 1973, a selective tuberculosis screening project was implemented. Screening of a "target group" of the population, 519 former miners, greater than or equal to 50 years of age, resulted in the discovery of abnormal chest X-rays in 182; (103 with silicosis, 36 with silicotuberculosis, 12 with inactive tuberculosis, and 31 with other abnormalities). Eighty-five of these persons had positive tuberculin skin tests. Preventive therapy was recommended for 50, and 36 completed the prescribed course of treatment. Eight new bacteriologically confirmed cases of tuberculosis were found and treated. A large number of persons (1,904) residing in the same area who were not part of the target group were also screened for tuberculosis. This group contained a large number of positive tuberculin reactors but very few were candidates for isoniazid preventive therapy. Thirteen persons in this group had abnormal chest X-rays consistent with inactive tuberculosis but 12 had been identified and given preventive therapy before the project began. These data suggest that selective approaches to screening for tuberculosis in a community which are based on an in-depth retrospective review of the tuberculosis case register can be highly successful.

Aged↗