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Biomedical subjects

J C Wilson

Publications and source records attributed to J C Wilson.

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

Catalysis by a new sialidase, deaminoneuraminic acid residue-cleaving enzyme (KDNase Sm), initially forms a less stable alpha-anomer of 3-deoxy-D-glycero-D-galacto-nonulosonic acid and is strongly inhibited by the transition state analogue, 2-deoxy-2, 3-didehydro-D-glycero-D-galacto-2-nonulopyranosonic acid, but not by 2-deoxy-2,3-didehydro-N-acetylneuraminic acid.

Deaminoneuraminic acid residue-cleaving enzyme (KDNase Sm) is a new sialidase that has been induced and purified from Sphingobacterium multivorum. Catalysis by this new sialidase has been studied by enzyme kinetics and 1H NMR spectroscopy. Vmax/Km values determined for synthetic and natural substrates of KDNase Sm reveal that 4-methylumbelliferyl-KDN (KDNalpha2MeUmb, Vmax/Km = 0.033 min-1) is the best substrate for this sialidase, presumably because of its good leaving group properties. The transition state analogue, 2, 3-didehydro-2,3-dideoxy-D-galacto-D-glycero-nonulosonic acid, is a strong competitive inhibitor of KDNase Sm (Ki = 7.7 microM versus Km = 42 microM for KDNalpha2MeUmb). 2-Deoxy-2, 3-didehydro-N-acetylneuraminic acid and 2-deoxy-2, 3-didehydro-N-glycolylneuraminic acid are known to be strong competitive inhibitors for bacterial sialidases such as Arthrobacter ureafaciens sialidase; however, KDNase Sm activity is not significantly inhibited by these compounds. This observation suggests that the hydroxyl group at C-5 is important for recognition of the inhibitor by the enzyme. Reversible addition of water molecule (or hydroxide ion) to the reactive sialosyl cation, presumably formed at the catalytic site of KDNase Sm, eventually gives rise to two different adducts, the alpha- and beta-anomers of free 3-deoxy-D-glycero-D-galacto-nonulosonic acid. 1H NMR spectroscopic studies clearly demonstrate that the thermodynamically less stable alpha-form is preferentially formed as the first product of the cleavage reaction and that isomerization rapidly follows, leading to an equilibrium mixture of the two isomers, the beta-isomer being the major species at equilibrium. Therefore, we propose that KDNase Sm catalysis proceeds via a mechanism common to the known exosialidases, but the recognition of the substituent at C-5 by the enzyme differs.

Flavobacterium↗
PubMed1997

Platelet-derived growth factor in human brain tumors.

This paper initially reviews ligand and receptor systems for the PDGF family and the signalling systems they use as well as their role in neural developments. It then describes the putative role of this family in astrocytoma, meningioma, and pituitary adenoma pathogenesis. Potential therapies with receptor antagonists or dominant negative mutants are discussed in the final sections.

Animals↗
PubMed1997

Patterns of differentiation among wild rabbit populations Oryctolagus cuniculus L. in arid and semiarid ecosystems of north-eastern Australia.

Feral rabbit populations in Australia have generally been managed using localized control procedures. While these procedures may result in local extinctions, persistence of populations will depend on the probability of recolonization. Genetic markers developed using temperature gradient gel electrophoresis (TGGE) combined with heteroduplex analysis (HA) of mitochondrial DNA (mtDNA) were used to characterize the degree of subdivision and extent of gene flow within and among rabbit populations distributed over large distances (up to 1000 km) in southern Queensland (QLD) and north-west New South Wales (NSW), Australia. TGGE analyses revealed significant heterogeneity in mtDNA control region haplotype frequencies. From heterogeneity chi 2 tests, it was evident that the differentiation observed was largely attributable to five sites which were located in the semiarid eastern region, whereas haplotype frequencies were homogeneous throughout the arid western region. These results suggest that there are independent population systems within the study area. The extent of gene flow among local populations within each system is related to the spatial configuration of acceptable habitat patches and the persistence of the populations is determined by the probability of recolonization following local extinction. These data suggest that to provide better overall control of rabbit populations, different management strategies may be necessary in arid and semiarid ecosystems. In arid south-west QLD and north-west NSW, where extensive gene flow occurs over large distances, rabbit populations should be managed at a regional level. In semiarid eastern QLD, where gene flow is restricted and populations are more isolated, localized control procedures may provide effective short-term relief. These results indicate that in nonequilibrium systems with patchy distribution of individuals, the interpretation of migration rate from estimates of gene flow obtained using existing genetic models must include an understanding of the spatial and temporal scales over which population processes operate.

Animals↗
PubMed1996

The binding of carbon monoxide and nitric oxide to leghaemoglobin in comparison with other haemoglobins.

Haemoglobins have the ability to discriminate between oxygen and other diatomic molecules. To further understanding of this process the X-ray crystal structures of carbonmonoxy and nitrosyl-leghaemoglobin have been determined at 1.8 A resolution. The ligand geometry is discussed in detail and the controversial issue of bent versus linear carbon monoxide binding is addressed. The bond angle of 160 degrees for CO-leghaemoglobin is in conflict with recent spectroscopy results on myoglobin but is consistent with angles obtained for myoglobin X-ray crystal structures. In contrast to the numerous carbon monoxide studies, very little stereochemical information is available for the nitric oxide adduct of haemoglobin. This is provided by the X-ray structure of NO-leghaemoglobin, which conforms to expected geometry with an Fe-NO angle of 147 degrees and a lengthened iron-proximal histidine bond. Thus crystallographic evidence is given for the predicted weakening of this bond on the binding of nitric oxide.

Binding Sites↗
PubMed1996

The crystal structures of trout Hb I in the deoxy and carbonmonoxy forms.

We have determined the X-ray crystallographic structure of trout Hb I in both the deoxy and carbonmonoxy forms to resolution limits of 2.3 angstroms and 2.5 angstroms, respectively. The overall fold of the molecule is highly similar to that of human HbA despite the low level of sequence identity between these proteins. Trout Hb I is unusual in displaying almost no pH dependence of oxygen binding affinity, and (at most) very weak interactions with heterotropic effector ligands such as organic phosphates. Comparison of the two quaternary states of the protein indicates how such effects are minimised and how the low-affinity T state of the protein is stabilised in the absence of heterotropic interactions.

Allosteric Regulation↗
PubMed1996

A 1H NMR investigation of the hydrolysis of a synthetic substrate by KDN-sialidase from Crassostrea virginica.

The mechanism of hydrolysis of 4-methylumbelliferyl 3-deoxy-D-glycero-alpha-D-galacto-2-nonulopyranosidonic acid (KDN alpha 2MeUmb, 4) by KDN-sialidase isolated from the hepatopancreas of the oyster Crassostrea virginica has been monitored by 1H NMR spectroscopy. The results of these experiments reveal that KDN-sialidase catalyses the hydrolysis of the synthetic substrate KDN alpha 2MeUmb, with initial release of alpha-D-KDN. This is consistent with an overall mechanism for the hydrolysis which proceeds with retention of anomeric configuration. These results agree with earlier NMR studies of other N-acetylneuraminic acid-recognising sialidases from both viral and bacterial sources.

Animals↗
PubMed1996

Limited genetic differentiation among wild Oryctolagus cuniculus L. (rabbit) populations in arid eastern Australia.

A systems approach is necessary for effective control of feral rabbit (Oryctolagus cuniculus L.) populations in the arid environments of Australia. Localized control procedures may result in local extinctions, but the persistence of the overall population will depend on the probability of recolonization, and hence, the degree of isolation of each local population unit. Genetic markers obtained using allozyme electrophoresis, temperature gradient gel electrophoresis (TGGE) and heteroduplex analysis (HA) were used to characterize the degree of structuring and extent of gene flow among rabbit populations in arid Queensland, Australia. Allozyme allele frequency data showed that there was no significant differentiation among sites (average FST = 0.005) and no isolation-by-distance or environmental discontinuity effects. TGGE/HA results also revealed no significant differentiation in mitochondrial DNA Control Region haplotype frequencies among sites and low interpopulation nucleotide divergence estimates (NST = 0.013). Therefore, rabbit populations exhibited a high degree of gene flow over large geographical areas (1600 km2) and were essentially a single panmictic unit. Unpredictable environmental conditions together with the spatial configuration of habitats which possess different probabilities of extinction may have resulted in repeated local extinctions followed by recolonization and homogenizing gene flow. These data suggest that current rabbit control strategies based on individual warren management may not achieve effective control in arid Queensland.

Alleles↗
PubMed1995

The structure of deoxy- and oxy-leghaemoglobin from lupin.

The leghaemoglobins have oxygen affinities 11 to 24 times higher than that of sperm whale myoglobin, due mainly to higher rates of association. To find out why, we have determined the structures of deoxy- and oxy-leghaemoglobin II of the lupin at 1.7 A resolution. Results confirm the general features found in previous X-ray analyses of this protein. The unique feature that has now emerged is the rotational freedom of the proximal histidine. In deoxy-leghaemoglobin the imidazole oscillates between two alternative orientations, eclipsing either the lines N1-N3 or N2-N4 of the porphyrin; in oxy-leghaemoglobin it is fixed in a staggered orientation. The iron atom moves from a position 0.30 A from the plane of the pyrrole nitrogen atoms in deoxy- to a position in the plane in oxy-leghaemoglobin while the Fe- bond distance remains constant at 2.02 A. The Fe-O-O angle is 152 degrees, as in human haemoglobin. The oxygen is hydrogen-bonded to the distal histidine at N epsilon 2-O1 and N epsilon 2-O2 distance of 2.95 A and 2.68 A, respectively. The porphyrin is ruffled equally in deoxy- and oxy-leghaemoglobins, due to rotations of the pyrrols about the N-Fe-N bonds, causing the methine bridges to deviate by up to 0.32 A from the mean porphyrin plane. The only feature capable of accounting for the high on-rate of the reaction with oxygen are the mobilities of the proximal histidine and distal histidine residues in deoxy-leghaemoglobin. The eclipsed positions of the proximal histidine in deoxy-leghaemoglobin maximize steric hindrance with the porphyrin nitrogen atoms and minimize pi-->p electron donation, while its staggered position in oxy-leghaemoglobin reverses both these effects. Together with the oscillation of the imidazole between the two orientations, these two factors may reduce the activation energy for the reaction of leghaemoglobin with oxygen. The distal histidine is in a fixed position in the haem pocket in the crystal, but must be swinging in and out of the pocket at a high rate in solution to allow the oxygen to enter.

Crystallography, X-Ray↗
PubMed1994

A determination of the solution conformation of the nonmammalian tachykinin eledoisin by NMR and CD spectroscopy.

The nonmammalian tachykinin eledoisin was investigated by use of CD and two-dimensional NMR techniques. In aqueous solution the peptide is conformationally averaged, but on addition of 50% trifluoroethanol (TFE) or sodium dodecyl sulfate (SDS) it adopts an alpha-helical structure. In TFE/H2O and SDS, residues 6-10 of eledoisin show more conformational order than the terminal regions, which undergo dynamic fraying. A possible turn in the N-terminal "address" region, the putative receptor recognition site of the peptide, is detected by NMR spectroscopy but appears to undergo substantial conformational averaging. The NMR data indicate that the helical central core of eledoisin is better defined in the micellar environment than in TFE; however, partial unfolding via 3(10) intermediates occurs in both cases. The conformational preference for SDS-bound eledoisin was examined by three-dimensional structure calculations using NMR-derived distance information in simulated annealing calculations.

Amino Acid Sequence↗
PubMed1992

A New Zealand randomized comparative study of three IUDs (Nova-T, MLCu375, MLAgCu250): 1-, 2- and 3-year results.

A randomized comparative study was made in New Zealand of 3 models of copper IUDs, the Nova-T, MLCu375 and MLAgCu250, with interval acceptors. Completing 3 years of use, there were 608 Nova-T (14,011 woman-months), 586 MLCu375 (14,161 woman-months) and 596 MLAgCu250 (14,614 woman-months). At 3 years, loss to follow-up was 5.2% for the Nova-T, 5.1% for the MLCu375 and 4.1% for the MLAgCu250. The Multiloads were significantly easier to insert and were preferred by the operators, as the insertion technique for the Nova-T was complicated. However, the Nova-T was significantly easier to remove. There was one perforation with a Nova-T in a puerperal breastfeeding woman. In the only 2 parameters that are comparable between series, accidental pregnancy and expulsion [1], the Multiloads have been shown to be superior with higher relevant continuation rates. At 3 years, the MLCu375 had a significantly lower accidental pregnancy rate and higher relevant continuation rate. The results obtained with the Nova-T are similar to those of the WHO study [2]. The MLCu375, with its potential for use up to 5 years, has been shown to be the superior device.

Contraception↗
PubMed1992

Rapid filtration assays for protein kinase C activity and phorbol ester binding using multiwell plates with fitted filtration discs.

In the conventional approach protein kinase activity and phorbol ester binding associated with protein kinase C (PKC) are measured by initially incubating samples in either test tubes or multiwell plates, followed by filtration of the terminated reaction mixture using either a manifold filtration device or a cell harvester. Here we report a method in which both the incubations and filtrations necessary for the determination of either protein kinase activity or phorbol ester binding are carried out in the same multiwell plate with fitted filtration discs made of polyvinylidene difluoride (Durapore membrane). Due to the very low binding of protein to these filters, there is no interference caused by these filters during the incubation period of the assays. The drawback with these filters compared to commonly used cellulose acetate membrane filters is that they retain less of the phosphate acceptor substrate histone H1 (only 15%) if filtered and washed with standard 5% trichloroacetic acid. However, this can be overcome by increasing the trichloroacetic acid concentration to 25% during filtration. For phorbol ester binding determinations, the samples are incubated with [3H]phorbol 12,13-dibutyrate in the microwells, the ligand bound PKC is adsorbed onto DEAE-Sephadex beads, and the beads then are filtered and washed in the same microwells. Furthermore, this multiwell filtration approach can also be adopted to previously described cytosolic phorbol ester receptor assays, which have the broader conditions for optimal binding to receptors. Durapore membrane filters are found to work well for punching into scintillation vials and there is complete recovery of the radioactivity retained with the filters. In the protein kinase assay the background radioactivity is very low (< 200 cpm) and in the phorbol ester binding assay the nonspecific binding is less than 1%. Thus, these low background values result in at least a fourfold increase in sensitivity for these assays. Since the incubations and filtrations are carried out in the same well without any transfer of the sample, the coefficient of variation in multiple determinations is found to be low. Furthermore, this method is rapid and more convenient for analyzing a larger number of samples than conventional methods which use test tubes, and it is less expensive to set up compared to the automated methods that use a cell harvester.

Animals↗
PubMed1989

A randomized comparative study of three IUDs: Nova-T, MLCu375 and MLAgCu250 in New Zealand: 1-year results.

A randomized comparative study was made in New Zealand of three models of copper IUDs, the Nova-T, MLCu375 and MLAgCu250, with interval acceptors. At 1 year, the Multiloads (MLs) had lower net termination rates for accidental pregnancy, expulsion, pain/bleeding, other medical removals and infections (use-related terminations) than the Nova-T. These rates were significantly lower for the MLAgCu250 than the Nova-T for accidental pregnancy, expulsion and infection. The MLCu375 had significantly fewer removals for pain/bleeding and for other medical removals than the Nova-T. The MLAgCu250 had a significantly lower accidental pregnancy rate than the MLCu375. The Multiloads had significantly higher relevant use-related continuation rates than the Nova-T.

Adult↗
PubMed1989

A prospective New Zealand study of fertility after removal of copper intrauterine contraceptive devices for conception and because of complications: a four-year study.

A prospective New Zealand study was started in 1982 to determine fertility rates and pregnancy outcomes after removal of copper intrauterine contraceptive devices to allow conception or because of complications. In a combined 4-year study, there were 887 removals to allow conception and 164 due to complications. Participants were 375 (35.7%) nulligravid and 676 (64.3%) gravid women. Within 48 months, 91.5% of the nulligravid and 95.7% of the gravid women had conceived. A 2-year combined study, with regard to longer use of intrauterine contraceptive devices (greater than 2 years), did not show any significant reduction in fertility or increase in ectopic gestation within 24 months. However, in gravid women of similar age distribution, there was a significant increase in the miscarriage rate, compared with use of intrauterine contraceptive devices for less than 2 years or compared with nulligravid women. In a 1-year study, removals because of complications did not cause a significant reduction in fertility or an increase in ectopic gestation, miscarriage, or preterm delivery rates within 12 months, compared with removals to allow conception.

Abortion, Spontaneous↗
PubMed1983

Faculty development for clinical instructors in allied health: an inservice approach.

Allied health faculty in the clinical setting are traditionally practitioners with both service and teaching responsibilities. Much effort is expended on ensuring quality performance by the practitioner in his or her health care specialty with little emphasis on the faculty member's preparation for teaching. This article describes an inservice program designed to provide applied teaching techniques for clinical faculty members faced with such a situation. The inservice program addresses four areas of interest to clinical faculty: orientation to the educational process, development and implementation of behavioral objective, selection of the most effective clinical teaching method, and evaluation of student clinical performance. The effectiveness of the inservice program in meeting its objectives was estimated by use of gain scores between pre- and posttest performance.

Allied Health Personnel↗
PubMed1982

Premature rupture of membranes prior to term: consequences of nonintervention.

Consequences of nonintervention in the management of prematurely ruptured membranes prior to term were assessed in 143 maternal charts and 145 corresponding infant records during a 2-year period. Patients were hospitalized at bed rest and were not given tocolytics or steroids. Antibiotics were used only when clinical examination indicated infection. Labor was induced in 13 patients. Time in utero was extended 1 week or more in 19% of cases. Maternal infection was identified in 15 women, all of whom recovered. There were 18 neonatal deaths and 4 stillbirths in the series. Three deaths might have been prevented by earlier delivery. Nonintervention in the management of premature rupture of the membranes did not have adverse effects on the incidence of maternal or neonatal infection but was relatively ineffectual in achieving significant extensions of time in utero

Anti-Bacterial Agents↗