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Biomedical subjects

M Stewart

Publications and source records attributed to M Stewart.

At least 343 records · Page 19Linked to original sources
PubMed1990

Structural and chemical characterization of the S layer of a Pseudomonas-like bacterium.

Sections and freeze-fractured preparations showed an S layer on the surface of Pseudomonas-like strain EU2. Polyacrylamide gel electrophoresis of cell envelopes extracted with 1% sodium dodecyl sulfate (SDS) at room temperature showed three proteins (45K, 55K, and 110K). The 55K protein was identified as the S-layer protein. Incubation in 1.5 M guanidine hydrochloride removed the S layer from cell envelopes and dissociated the structure into subunits. The soluble 55K protein reassembled into planar sheets upon removal of the guanidine hydrochloride by dialysis. Electron microscopy and image processing indicated that these sheets had p4 symmetry in projection with a lattice constant of 13.2 +/- 0.1 nm (corresponding to 9.3 nm between adjacent fourfold axes). In some instances these reassemblies appeared to form small three-dimensional crystals which gave particularly clear views of the structure in projection because of the superimposition of information from a number of layers. A model is proposed with molecules having rounded lobes connected by a narrower linker region and joining at the lobes to form the fourfold axes of the array. The pattern superficially resembles those of other bacterial S layers, such as those of Aeromonas salmonicida, Aeromonas hydrophila, and Azotobacter vinelandii. Extraction of cell envelopes with 1% SDS at 50 degrees C released the 110K protein from the envelopes and removed an amorphous backing layer from the S layer. The 45K protein displayed heat-modifiable migration in SDS-polyacrylamide gel electrophoresis and was insoluble in SDS at 50 degrees C or in high concentrations of guanidine hydrochloride, suggesting that it was associated with the peptidoglycan.

Bacteria↗
PubMed1990

Selective digestion of nuclear envelopes from Xenopus oocyte germinal vesicles: possible structural role for the nuclear lamina.

We have used enzymic digestion as a structural probe to investigate components of the nuclear envelope of germinal vesicles from Xenopus oocytes. Previous studies have shown that these envelopes are composed of a double membrane in which nuclear pore complexes are embedded. The nuclear pore complexes are linked to a fibrous lamina that underlies the nucleoplasmic face of the envelope. The pores are also linked by pore-connecting fibrils that attach near their cytoplasmic face. Xenopus oocyte nuclear envelopes were remarkably resistant to extraction with salt solutions and, even after treatment with 1 M NaCl or 3 M MgCl2, pores, lamina and pore-connecting fibrils remained intact. However, mild proteolysis with trypsin selectively removed the lamina fibres from Triton-extracted nuclear envelopes to leave only the pore complexes and connecting fibrils. This observation confirmed that the pore-connecting fibrils were different from the lamina fibres and were probably constructed from different proteins. Trypsin digestion followed by Triton treatment resulted in the complete disintegration of the nuclear envelope, providing direct evidence for a structural role for the lamina in maintaining envelope integrity. Digestion with ribonuclease did not produce any marked change in the structure of Triton-extracted nuclear envelopes, indicating that probably neither the pore-connecting fibrils nor the cytoplasmic granules on the pore complexes contained a substantial proportion of RNA that was vital for their structural integrity.

Animals↗
PubMed1990

Identification of time-compressed sentential stimuli by good vs poor readers.

Ability of eight good and eight poor readers (in Grade 1, ages ranging from 6.7 to 7.4 yr.) to discriminate phonemic contrasts presented in 50% time-compressed sentential stimuli (Subtest 13 of the Carrow-Auditory Visual Abilities Test) was measured. Good readers exhibited a significantly higher over-all mean performance than poor readers on the time-compressed task. Effects of time-compression on the perception of manner, place, voicing and frequency contrasts showed a similar pattern of errors for both groups of readers. Implications of the effects of auditory discrimination on reading abilities are discussed.

Arousal↗
PubMed1989

Detection of an atropine-resistant component of the hippocampal theta rhythm in urethane-anesthetized rats.

An important pharmacological feature of the hippocampal theta rhythm in urethane-anesthetized animals is its apparent sensitivity to antimuscarinic drugs. This sensitivity may be partly due to a masking of the theta frequency by increases in both higher and lower frequency EEG components that are unrelated to any residual theta rhythm. The discovery of atropine-resistant, rhythmic medial septal neurons has provided a physiological trigger for averaging EEG and unit activity after large atropine doses. Such averaging has permitted the detection of an atropine-resistant component of the hippocampal theta rhythm in urethane-anesthetized rats. The postatropine theta activity recorded from both CAl (superficial to the pyramidal cell layer) and dentate (near the hippocampal fissure) in 15 rats was typically reduced in amplitude, but the recordings from the two locations maintained their phase relations to the septal units and to each other. The presence of this residual theta component after doses as large as 100 mg/kg indicates that it cannot be mediated by muscarinic cholinergic receptors. The coupling of the signal to the atropine-resistant septal cells strengthens our previous suggestion that these septo-hippocampal neurons are not cholinergic, and are therefore probably GABAergic.

Anesthesia↗
PubMed1989

Smoking and occupational allergy in workers in a platinum refinery.

OBJECTIVE: To test the hypothesis that smoking increases the risk of sensitisation by occupational allergens. DESIGN: Historical prospective cohort study. SETTING: Platinum refinery. SUBJECTS: 91 Workers (86 men) who started work between 1 January 1973 and 31 December 1974 and whose smoking habit and atopic state (on skin prick testing with common allergens) had been noted at joining. MAIN OUTCOME MEASURES: Results of skin prick tests with platinum salts carried out routinely every three to six months and records of any respiratory symptoms noted by the refinery's occupational health service. Follow up was until 1980 or until leaving refinery work, whichever was earlier. RESULTS: 57 Workers smoked and 29 were atopic; 22 developed a positive result on skin testing with platinum salts and 49 developed symptoms, including all 22 whose skin test result was positive. Smoking was the only significant predictor of a positive result on skin testing with platinum salts and its effect was greater than that of atopy; the estimated relative risks (95% confidence interval) when both were included in the regression model were: smokers versus non-smokers 5.05 (1.68 to 15.2) and atopic versus non-atopic 2.29 (0.88 to 5.99). Number of cigarettes smoked per day was the only significant predictor of respiratory symptoms. CONCLUSION: Smokers are at increased risk of sensitisation by platinum salts.

Adolescent↗
PubMed1989

Firing relations of medial septal neurons to the hippocampal theta rhythm in urethane anesthetized rats.

On the basis of spontaneous firing patterns and relations to the hippocampal theta rhythm, three cell types were identified within the medial septal nucleus and vertical limb of the nucleus of the diagonal band of Broca (MSN-NDB). In addition to the well known rhythmically bursting cells that fired in bursts on each cycle of the hippocampal theta rhythm, two other cell types are distinguished. "Clock" cells fired at high rates with a very regular, periodic firing pattern that was unrelated to the theta rhythm. "Irregular" cells fired at much lower rates, especially during theta rhythm, and had a pseudo-random firing pattern. The firing of "irregular" cells was often significantly phase-locked to the hippocampal theta rhythm. Crude estimates of the relative proportions of these cell types suggest that the rhythmically bursting cells comprise about 75% of the cells of the MSN-NDB. These three cell types bear a remarkable resemblance, in firing patterns and relative proportions, to the three principal cell types of the medial septal nuclei described in the freely moving rat (Ranck 1976). Measurements of the preferred phases of firing of 128 rhythmically bursting septal neurons (including 22 atropine-resistant and 11 atropine-sensitive cells) indicate that there is no single preferred phase of firing for the population. Rather the distribution of phases over the theta cycle is statistically flat. Variations in recording locations cannot account for this distribution since large differences in preferred phase were found for pairs of cells at the same location. Similarly, plotting only the group of cells identified as projection cells by antidromic activation from the fimbria/fornix, failed to reveal a peak in the distribution. In contrast to the rhythmically bursting cells, the distribution of preferred firing phases for the "irregular" cells with a significant phase-locking to the theta rhythm did have a clear peak. The peak occurred near the dentate theta rhythm positivity, consistent with the hypothesis that they are driven by feedback from CA1 complex-spike cells.

Action Potentials↗
PubMed1989

Effects of a health education campaign for the earlier diagnosis of melanoma.

As part of a national campaign to combat the rising incidence of and mortality from cutaneous malignant melanoma, a programme of improved clinical services and professional and public education was set up in Nottingham in January to July 1987. The public education campaign in July led to an immediate increase in the weekly number of referrals to the pigmented lesion clinic from 10 to 54. The effect on general practitioner workload was less dramatic, the weekly number of consultations for discrete pigmented lesions rising from 0.5 to 3. In materials sent to GPs, we recommended that patients with three or more of seven specified signs should be referred for specialist opinion. Only 40% of the patients referred to the pigmented lesion clinic fulfilled this criterion, but 6% of these patients had a melanoma, compared to only 0.4% of those who did not meet the criterion. In the 6 months following the campaign, 64% of melanomas diagnosed in Nottingham residents had a Breslow thickness of less than 1.5 mm whereas only four (16%) were greater than 3.5 mm. However, this distribution was not significantly different from that seen in the three and a half years before the campaign. These results suggest that attempts to improve early diagnosis of the disease by health education are justified, but, in view of the service implications, full evaluation of such campaigns by large scale and long-term studies is essential. Future campaigns should give greater stress to referral criteria.

England↗
PubMed1989

Molecular interactions in paracrystals of a fragment corresponding to the alpha-helical coiled-coil rod portion of glial fibrillary acidic protein: evidence for an antiparallel packing of molecules and polymorphism related to intermediate filament structure.

We have expressed in Escherichia coli a fragment of c-DNA that broadly corresponds to the alpha-helical coiled-coil rod section of glial fibrillary acidic protein (GFAP) and have used the resultant protein to prepare paracrystals in which molecular interactions can be investigated. An engineered fragment of mouse GFAP c-DNA was inserted into a modified version of the E. coli expression vector pLcII, from which large quantities of a lambda cII-GFAP rod fusion protein were prepared. A protein fragment corresponding to the GFAP rod was then obtained by proteolysis with thrombin. Paracrystals of this material were produced using divalent cations (Mg, Ca, Ba) in the presence of a chaotrophic agent such as thiocyanate. These paracrystals showed a number of polymorphic patterns that were based on a fundamental pattern that had dyad symmetry and an axial repeat of 57 nm. Analysis of both positive and negative staining patterns showed that this fundamental pattern was consistent with a unit cell containing two 48-nm-long molecules in an antiparallel arrangement with their NH2 termini overlapping by approximately 34 nm. More complicated patterns were produced by stacking the fundamental pattern with staggers of approximately 1/5, 2/5, and 1/2 the axial repeat. The molecular packing the unit cell was consistent with a range of solution studies on intermediate filaments that have indicated that a molecular dimer (i.e., a tetramer containing four chains or two coiled-coil molecules) is an intermediate in filament assembly. Moreover, these paracrystals allow the molecular interactions involved in the tetramer to be investigated in some detail.

Animals↗
PubMed1989

The Dictyostelium gelation factor shares a putative actin binding site with alpha-actinins and dystrophin and also has a rod domain containing six 100-residue motifs that appear to have a cross-beta conformation.

The 120-kD gelation factor and alpha-actinin are among the most abundant F-actin cross-linking proteins in Dictyostelium discoideum. Both molecules are homodimers and have extended rod-like configurations that are respectively approximately 35 and 40 nm long. Here we report the complete cDNA sequence of the 120-kD gelation factor which codes for a protein of 857 amino acids. Its calculated molecular mass is 92.2 kD which is considerably smaller than suggested by its mobility in SDS-PAGE. Analysis of the sequence shows a region that is highly homologous to D. discoideum alpha-actinin, chicken fibroblast alpha-actinin, and human dystrophin. This conserved domain probably represents an actin binding site that is connected to the rod-forming part of the molecule via a highly charged stretch of amino acids. Whereas the sequence of alpha-actinin (Noegel, A., W. Witke, and M. Schleicher. 1987. FEBS [Fed. Eur. Biochem. Soc.] Lett. 221:391-396) suggests that the extended rod domain of the molecule is based on four spectrin-like repeats with high alpha-helix potential, the rod domain of the 120-kD gelation factor is constructed from six 100-residue repeats that have a high content of glycine and proline residues and which, in contrast to alpha-actinin, do not appear to have a high alpha-helical content. These repeats show a distinctive pattern of regions that have high beta-sheet potential alternating with short zones rich in residues with a high potential for turns. This observation suggests that each 100-residue motif has a cross-beta conformation with approximately nine sheets arranged perpendicular to the long axis of the molecule. In the high beta-potential zones every second residue is often hydrophobic. In a cross-beta structure, this pattern would result in one side of the domain having a surface rich in hydrophobic side chains which could account for the dimerization of the 120-kD gelation factor subunits.

Actinin↗
PubMed1989

Post-traumatic parotid fistulae and sialoceles. A prospective study of conservative management in 51 cases.

The management of parotid sialoceles and fistulae have been unsatisfactory in the past, and numerous methods of treatment with varying success and morbidity have been described. The present prospective study reports results of conservative therapy in 51 patients over a 3-year period. In 50 patients, the injury healed upon conservative management. During the early phase of the study, a limited conservative regimen through which the patients received nothing orally for 5 days only was used. During the latter part of the study, patients were administered nothing orally until complete healing of the injury. In terms of the time it took for healing of the injury, the differences of the two regimens (24 +/- 4 vs. 9.4 +/- 0.9 days) was highly significant (p less than 0.001). The response to conservative management depended on the severity of injury as demonstrated by sialography. Injury to minor intraparotid ducts (G1) healed in significantly less time compared with that to a major intraparotid duct (G2) or ductal injuries (p less than 0.001). There was no difference between the healing of G2 injury (10.3 +/- 1.8 days) and partial ductal transections (10.5 +/- 2.2 days) (p greater than 0.05). There was a significantly greater delay in healing with complete duct transections (21.5 +/- 3.7 days) compared with partial duct transections and G2 injuries (10.2 +/- 2.1 days) (p less than 0.01). There was no difference in the mean period for healing between salivary fistulae and sialoceles (p greater than 0.05). It is concluded that a new classification of parotid fistulae based on sialographic findings has prognostic and therapeutic value. Furthermore, the excellent results achieved with conservative therapy in this study suggest that it may be the initial treatment of choice for parotid fistulae.

Acute Disease↗
PubMed1989

Postponing pregnancy after perinatal death: perspectives on doctor advice.

The Perinatal Loss Interview was administered to 24 mothers who had experienced perinatal loss and were raising a child born subsequent to the loss; mothers were asked about postponing subsequent pregnancy, including what their doctors advised. Mothers were dissatisfied with doctor advice, reporting that the timing of a subsequent pregnancy was a personal decision and many factors influenced their decision. Furthermore, regardless of timing, most mothers reported overprotective and replacement feelings toward the subsequent child. These results imply that physicians may be most effective by educating mothers about advantages and disadvantages of postponing pregnancy so that an informed decision can be made.

Adaptation, Psychological↗
PubMed1989

Patterns of colonisation of Campylobacter pylori in the oesophagus, stomach and duodenum.

Thirty five subjects underwent upper gastrointestinal endoscopy and multiple biopsy (30 patients, five normal subjects). A total of 11 biopsies per subject from four sites (oesophagus (three), gastric body (two), antrum (three), duodenum (three] were examined for inflammation and the presence of Campylobacter pylori and using standard methods of culture and by light (LM) and electron microscopy (EM). The organism was cultured from oesophageal biopsies in eight of 30 (27%) patients but could not be identified at this site by LM or EM. There was evidence of oesophageal inflammation in 20 patients which was associated with the local finding of C pylori in five (25%) including two of seven (29%) with Barrett's mucosa. Antral C pylori was present in 22 of 23 (96%) patients with chronic active gastritis. The organism was found in the antrum and oesophagus in four of 22 patients (18%), in the antrum and duodenum in four of 22 patients (18%) and in all three sites in a further two of 22 patients (9%). Antral C pylori was found in five of six patients with peptic ulceration. C pylori was cultured from the duodenum in six patients with confirmation by LN and EM in three, but only on areas of gastric metaplasia. The organism was not found in the normal group. This study indicates that C pylori may be irregularly isolated from the oesophagus and duodenum in patients with antral C pylori and chronic active gastritis. The role of C pylori in the oesophagus is most likely that of a commensal or contaminant.

Adult↗