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Biomedical subjects

J Keen

Publications and source records attributed to J Keen.

At least 19 recordsLinked to original sources
PubMed1995

Explaining variation in radiologists' reporting times.

This paper describes an investigation into the reasons for variation in the time taken by senior radiologists to complete radiological reports. An observational study of the reporting process at one UK hospital was undertaken for a 25 day period. An independent health service researcher observed the radiology reporting process and collected data on a variety of factors including the time taken to produce the report, the number and nature of all images viewed, the experience of the radiologist, and the number of disturbances that occurred. The nature of the variation in reporting time was explored using both simple comparative statistics and more sophisticated multiple regression techniques. Data were collected on 2345 report observations and the median report time was 117 s. This research provides the first empirical evidence for systematic variation in reporting time. The results confirm the importance of certain factors that were expected to explain report time variation. For example, the results indicate that report time tended to be significantly shorter in reporting sessions that were busy, and significantly longer when the radiologist was disturbed during the reporting process or was training juniors during a reporting session. More surprising were the results indicating that there was no significant difference in report time for reports categorized as urgent or "hot" and those categorized as less urgent or "cold", and that report time appeared to vary systematically depending on the day of the week and on the time of day.

Humans↗
PubMed1992

Eosinophil chemotactic peptide sequences in rat alpha-CGRP. Activation of a novel trophic action by neutral endopeptidase 24.11.

Rat alpha- and alpha-CGRP are substrates for endopeptidase 24.11 in vitro. Cleavage of both peptides occurs at several points, including an unusual substrate recognition site to the amino side of ala36. In alpha-CGRP this resulted in the early formation of val32-gly-ser-glu35, a sequence previously reported to be a component of the eosinophil chemotactic factor of anaphylaxis (ECF-A). The biological activity of this peptide fragment was confirmed by bioassay. Chemotactic activity in other hydrolysis fragments of both alpha- and beta-CGRP was observed. Both alpha- and beta-CGRP could thus serve as precursors to different eosinophil chemotactic peptide fragments. A novel function of endopeptidase 24.11 may be to modify rather than to terminate the biological activity of CGRP peptides.

Amino Acid Sequence↗
PubMed1992

Endopeptidase-24.11 cleaves a chemotactic factor from alpha-calcitonin gene-related peptide.

The sequence of rat alpha-calcitonin gene-related peptide (CGRP-alpha) contains the tetrapeptide eosinophil granulocyte chemotactic factor Val32-Gly-Ser-Glu35. Peptide fragments formed following hydrolysis of rat CGRP-alpha in vitro by endopeptidase-24.11 were identified. The tetrapeptide fragment was generated following cleavage at a substrate recognition site unusual for this enzyme (-Glu-Ala-). Chemotactic activity of rat CGRP-alpha was increased following hydrolysis. Furthermore, rat CGRP-beta, which lacks the tetrapeptide sequence and is completely devoid of chemotactic activity, displayed low but measurable activity after hydrolysis. Val-Gly-Ser-Glu was identified as the principle fragment with chemotactic activity in rat CGRP-alpha. The results show that the chemotactic activity of the neuropeptide rat CGRP-alpha towards eosinophil polymorphonuclear leukocytes is increased following its hydrolysis in vitro by endopeptidase 24.11 through the formation of a previously identified eosinophil chemotactic tetrapeptide.

Amino Acid Sequence↗
PubMed1992

Nursing power and practice in the United Kingdom National Health Service.

Over the last decade the National Health Service (NHS) in the United Kingdom has experienced major organizational change. Successive government initiatives designed to improve local management of hospitals have tended to marginalize nurses. Resource Management, a major initiative, which is the model adopted in the NHS Review for hospital management for the 1990s, appeared initially to offer nurses an opportunity to influence decision-making directly. In practice, nurses' experiences of Resource Management were mixed. This study of the six hospitals which piloted the introduction of Resource Management showed that nurses did not always grasp the opportunity to enhance their power and practice. There was evidence from the study that the introduction of information technology curbed innovations in practice, and removed nurses from patient care delivery.

Decision Making, Organizational↗
PubMed1991

Cardiovascular effects of endothelin in trout.

The cardiovascular effects of endothelin-1 (ET-1) in trout were examined in unanesthetized fish, perfused tissues, and isolated vascular rings. In vivo, a bolus of 500 ng/kg body wt ET-1 transiently lowered arterial (postgill) blood pressure (BP) by nearly 30%; 1,500 ng/kg body wt produced a triphasic, pressor-depressor-pressor, response. Continuous infusion of 0.1, 1, 10, and 30 ng.kg-1.min-1 progressively lowered BP but did not affect heart rate (HR), urine flow, or electrolyte excretion. In the in situ perfused heart ET-1 (10(-11) to 10(-8) M) had no effect on HR or power output. ET-1 produced dose-dependent increases in vascular resistance in the perfused gill, renal-skeletal muscle, and splanchnic circulations, and increased tension, independent of endothelium, in vascular rings from celiacomesenteric (CA) and coronary arteries and anterior cardinal veins (CV). Ventral aortas were refractory to ET-1. In vitro, ET-1 effects were slow in onset and long lasting. External calcium was required for maximal ET-1 responses in gill and CA. ET-1 effects on CA but not CV were partially inhibited by calcium channel blockers, diltiazem, and D 600, and by the guanylate cyclase activators, atrial natriuretic factor, and sodium nitroprusside. [3H]water flux across the perfused gill was stimulated by ET-1 through what appeared to be a vascular-independent mechanism. These experiments show that the trout vasculature is exquisitely sensitive to ET-1, and they suggest that the physiological expression of this peptide has been highly conserved during the course of vertebrate evolution.

Animals↗
PubMed1990

Nucleotide sequence of the engXCA gene encoding the major endoglucanase of Xanthomonas campestris pv. campestris.

The nucleotide sequence of the gene (engXCA) encoding the major extracellular endoglucanase (ENGXCA) of the phytopathogenic bacterium Xanthomonas campestris pv. campestris (X. c. campestris) was determined and compared with the N-terminal amino acid (aa) sequence of the purified enzyme. An open reading frame of 1479 bp encoding 493 aa was identified, of which the N-terminal 25 aa represent a potential signal peptide. Determination of the exact position of a Tn5 insertion within engXCA, which did not reduce the encoded enzyme activity, indicated that the C-terminal region of the protein is not crucial for ENGXCA activity. Comparison of the complete deduced aa sequence with those deduced from other endoglucanase- and exoglucanase-encoding genes revealed a region with a high degree of homology, located towards the C terminus of the protein. These data indicate that the X. c. campestris ENGXCA may have a domain structure similar to that of many other bacterial and fungal cellulolytic enzymes. Hydrophobic cluster analysis was performed on the deduced aa sequence. Comparison of this analysis with those of 30 other cellulase sequences belonging to six different families indicated that the X. c. campestris enzyme can be classified in family A. The two aa residues which had previously been identified as 'potentially catalytic' within this family of cellulases, are conserved in the X. c. campestris ENGXCA.

Amino Acid Sequence↗
PubMed1988

A new epitope on human myelin basic protein arising from cleavage by a metalloendoprotease associated with brain myelin membranes.

Human brain myelin membranes were incubated to allow activity of an associated metalloendoprotease which cleaves myelin basic protein (MBP). A 10.3 kDa C-terminal fragment of MBP, peptide C, isolated from the incubation medium had a blocked N-terminal. After treatment with pyroglutamyl aminopeptidase, N-terminal sequencing indicated that Gln74 of MBP formed the N-terminal residue of peptide C. A rabbit antiserum was raised to a synthetic peptide containing the sequence Pyroglu-Lys-Ser-His-Gly-Arg, corresponding to the first six residues of peptide C. By immunoblotting this serum reacted with peptide C but not with intact MBP. The data indicate that cleavage of MBP by a myelin-associated protease engenders a new epitope.

Amino Acid Sequence↗
PubMed1988

Deep-etch visualization of proteins involved in clathrin assembly.

Assembly proteins were extracted from bovine brain clathrin-coated vesicles with 0.5 M Tris and purified by clathrin-Sepharose affinity chromatography, then adsorbed to mica and examined by freeze-etch electron microscopy. The fraction possessing maximal ability to promote clathrin polymerization, termed AP-2, was found to be a tripartite structure composed of a relatively large central mass flanked by two smaller mirror-symmetric appendages. Elastase treatment quantitatively removed the appendages and clipped 35 kD from the molecule's major approximately 105-kD polypeptides, indicating that the appendages are made from portions of these polypeptides. The remaining central masses no longer promote clathrin polymerization, suggesting that the appendages are somehow involved in the clathrin assembly reaction. The central masses are themselves relatively compact and brick-shaped, and are sufficiently large to contain two copies of the molecule's other major polypeptides (16- and 50-kD), as well as two copies of the approximately 70-kD protease-resistant portions of the major approximately 105-kD polypeptides. Thus the native molecule seems to be a dimeric, bilaterally symmetrical entity. Direct visualization of AP-2 binding to clathrin was accomplished by preparing mixtures of the two molecules in buffers that marginally inhibit AP-2 aggregation and cage assembly. This revealed numerous examples of AP-2 molecules binding to the so-called terminal domains of clathrin triskelions, consistent with earlier electron microscopic evidence that in fully assembled cages, the AP's attach centrally to inwardly-directed terminal domains of the clathrin molecule. This would place AP-2s between the clathrin coat and the enclosed membrane in whole coated vesicles. AP-2s linked to the membrane were also visualized by enzymatically removing the clathrin from brain coated vesicles, using purified 70 kD, uncoating ATPase plus ATP. This revealed several brick-shaped molecules attached to the vesicle membrane by short stalks. The exact stoichiometry of APs to clathrin in such vesicles, before and after uncoating, remains to be determined.

Aluminum Silicates↗
PubMed1987

Pig kidney angiotensin converting enzyme. Purification and characterization of amphipathic and hydrophilic forms of the enzyme establishes C-terminal anchorage to the plasma membrane.

Angiotensin converting enzyme from pig kidney was isolated by affinity chromatography after solubilization from the membrane by one of four different procedures. Solubilization with Triton X-100, trypsin or by an endogenous activity in microvillar membranes all generated hydrophilic forms of the enzyme as assessed by phase separation in Triton X-114 and failure to incorporate into liposomes. Only when solubilization and purification was effected by Triton X-100 in the presence of EDTA (10 mM) could an amphipathic form of the enzyme (membrane- or m-form) be generated. The m-form of angiotensin converting enzyme (ACE) appeared slightly larger (Mr approx. 180,000) than the hydrophilic forms (Mr approx. 175,000) after SDS/polyacrylamide-gel electrophoresis, and the m-form incorporated into liposomes, consistent with retention of the membrane anchor. The m-form of ACE showed an N-terminal sequence identical with that of preparations of enzyme isolated after solubilization with detergent alone (d-form), with trypsin (t-form) or by the endogenous mechanism (e-form). These data imply that ACE is anchored to the plasma membrane via its C-terminus, in contrast with the N-terminal anchorage of endopeptidase-24.11. No release of ACE from the membrane could be detected with a variety of phospholipases, including bacterial phosphatidylinositol-specific phospholipases C, although an endogenous EDTA-sensitive membrane-associated hydrolase was capable of releasing a soluble, hydrophilic, form of the enzyme.

Amino Acid Sequence↗
PubMed1986

Sequencing and identification of a cDNA clone for tomato polygalacturonase.

The 2a isoenzyme of tomato polygalacturonase was purified from ripe fruit and characterised. The N-terminal amino acid sequence of the protein was determined in order to identify polygalacturonase cDNA clones. The nucleotide sequence of a ripening-related cDNA (pTOM 6) was determined and found to encode the N-terminal sequence of mature polygalacturonase 2a. The complete open reading frame encodes a polypeptide of molecular weight 50,051, including a putative pre-sequence of 71 amino acids.

Amino Acid Sequence↗
PubMed1985

Rainbow trout red cells in vitro.

Washed rainbow trout erythrocytes incubated at 14 degrees C in Eagle's minimal essential medium and Cortland saline displayed sharp reductions in volume and water content, nucleoside triphosphate, K+ and Cl- concentrations. Mg2+ and, to a lesser extent, Na+ concentrations increased. Cellular to medium Cl- ratios were indicative of membrane hyperpolarization. Morphological irregularities were also observed. Oxygen consumption and hemoglobin system organization were not grossly affected. Supplementation with pyruvate stabilized nucleoside triphosphate concentrations for at least 24 hr, and reduced rates of volume and compositional change to some extent. Addition of norepinephrine at physiologically realistic levels led to stabilization of Cl- content and reductions in Mg2+ accumulation and water loss. Transient but modest increases in K+ and Ca2+ were coupled, under these circumstances, with some decrease in Na+ concentration. Factors which may contribute to the dysfunctional status of these cells in vitro are discussed.

Animals↗
PubMed1984

Monoclonal antibodies that distinguish between human cellular and plasma fibronectin.

Two monoclonal antibodies have been developed against human fibronectin expressed by simian virus 40 transformed human mammary epithelial cells. Monoclonal antibody ICRF-FN-3 recognizes a determinant on human cellular but not plasma fibronectin. The antigenic site recognized by FN-3 is lost after limited proteolysis of cellular fibronectin with alpha-chymotrypsin but not trypsin. Monoclonal antibody, ICRF-FN-4, against a determinant on both human plasma and cellular fibronectin reacts with an antigenic site on fibronectin which is not destroyed by trypsin or alpha-chymotrypsin. Although the epitopes recognized by FN-3 and FN-4 are expressed similarly by cells from the human breast they are expressed differently on rat mammary (RAMA) cell lines.

Animals↗