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Biomedical subjects

L M Hall

Publications and source records attributed to L M Hall.

At least 19 recordsLinked to original sources
PubMed1992

Platelet dense granule release reaction monitored by high-performance liquid chromatography-fluorometric determination of endogenous serotonin.

The platelet dense granule release reaction was monitored by measuring the serotonin content of platelets collected by filtration following release. Sensitive HPLC-fluorometric analysis permitted release to be assessed using small (25-50 microliters) volumes of plasma and whole blood. Release could be examined for periods as short as 1 s due to the rapid stoppage effected by filtration. The half-life of thrombin-stimulated (1 U/ml) release was 2-3 s, the EC50 values observed for thrombin-stimulated release over a 60-s release period were 0.01-0.03 U/ml for diluted whole blood and plasma samples.

Blood Platelets↗
PubMed1992

Variation in egg yolk cholesterol concentration between and within breeds of the domestic fowl.

1. The pattern of variation for egg yolk cholesterol concentration between 5 commercial egg layer lines and a cross of Gallus domesticus is described. 2. Yolk cholesterol concentration in the cross was lower than in the lines, and 6.7% lower than the midparent value. 3. It is proposed that the reduced yolk cholesterol concentration of the cross may be a consequence of heterosis, although sex-linkage and/or maternal effects cannot be discounted. 4. The difference between the cross and parental lines is consistent with a physiological relationship between yolk cholesterol concentration and rate of egg production, but not between yolk cholesterol concentration and yolk weight.

Animals↗
PubMed1992

Survey of the prevalence of beta-lactamases amongst 1000 gram-negative bacilli isolated consecutively at the Royal London Hospital.

beta-Lactamase expression was examined in 1000 consecutive Gram-negative bacilli isolated from urine, wound swab, sputum or blood specimens received at the Microbiology Laboratory of the Royal London Hospital. This survey, performed between January and April, 1991, followed a similar study undertaken in early 1982. The distribution of species was similar in the two surveys, except that the proportion of Pseudomonas aeruginosa isolates had increased from 11% in 1982 to 17.5% in the present study. This increase was balanced by a decreased proportion of enterobacteria. Amongst plasmid-mediated beta-lactamases, TEM-1 (especially), TEM-2, SHV-1 and OXA types continued to predominate in enterobacteria. Their frequency in Escherichia coli was unchanged (46% in 1991 compared with 43% in 1982), but had increased from 5 to 22% amongst Proteus mirabilis isolates. An apparent decrease in their frequency amongst Enterobacter cloacae isolates, from 48% in 1982 to 17% in 1991, probably reflected changes to strain prevalence rather than enzyme prevalence. Plasmid type beta-lactamases were present in fewer than 2% of P. aeruginosa isolates in both surveys. In the present study, chromosomal beta-lactamase derepression (constitutive hyperproduction) was detected in 10/76 isolates of E. cloacae, Enterobacter aerogenes, Citrobacter freundii, Serratia spp. and Morganella morganii, and in 2/170 P. aeruginosa isolates. These proportions were increased, compared with those seen the 1982 survey, though the significance was borderline (P approximately 0.05; chi 2 test). Extended-spectrum plasmid mediated beta-lactamases, unknown in 1982, were found in 11/70 Klebsiellae pneumoniae isolates in the present study. Ten of these organisms, representing at least five distinct strains, produced TEM-10 enzyme, encoded by a plasmid of c. 90 kb; the remaining organism had an unidentified SHV-derived enzyme.

Anti-Bacterial Agents↗
PubMed1992

Typing of Enterococcus species by DNA restriction fragment analysis.

Enterococci are a frequent cause of hospital-acquired infection, being associated with urinary tract infections, wound sepsis, bacteremia, and endocarditis. The source of infection is usually thought to be endogenous, but some evidence points to cross-infection between patients. A better understanding of the epidemiology of enterococci has been limited by the lack of a good discriminatory typing system. This report describes the application of two DNA-based typing methods to Enterococcus faecalis and Enterococcus faecium: comparison of restriction fragments from total DNA by conventional electrophoresis and comparison of restriction fragments hybridizing to an rRNA gene probe (ribotyping). Comparison of restriction fragments (from SstI digestion) by conventional electrophoresis was simple and highly discriminatory. The results of analysis of blood culture isolates and of repeat isolates from individual patients are reported. Ribotyping (with BscI digestion) was more applicable at the level of species discrimination.

Bacteremia↗
PubMed1992

Epidemiology of Enterococcus faecalis urinary tract infection in a teaching hospital in London, United Kingdom.

Enterococcus faecalis is a frequent cause of urinary tract infection in hospitalized patients. Recent reports have suggested that the organism may frequently be acquired by cross-infection from other patients. In this study, we used total DNA restriction patterns to type 135 urine isolates of E. faecalis from four sets of patients. Isolates were placed into types (all bands identical) and into groups (most bands identical). Most isolates were discriminated by the typing method, and the results suggested that direct cross-infection occurred rarely if at all. However, two groups of clonally related isolates occurred frequently in the urine specimens and also in feces from hospital-associated patients and were often associated with antibiotic resistance. Isolates from these two groups were found less frequently in feces from people not associated with the hospital.

Cluster Analysis↗
PubMed1991

The acetylcholinesterase gene of Anopheles stephensi.

1. The acetylcholinesterase (AChE) gene from the important malaria vector Anopheles stephensi has been isolated by homology to the Drosophila acetylcholinesterase gene. 2. The complete sequence and intron-exon organization has been determined. The encoded protein has 69% identity to Drosophila AChE and 38 and 36% identity to Torpedo AChE and human butyrylcholinesterase, respectively.

Acetylcholinesterase↗
PubMed1991

Activity of clavulanate combinations against TEM-1 beta-lactamase-producing Escherichia coli isolates obtained in 1982 and 1989.

Recent reports of decreased susceptibility to amoxycillin/clavulanate and ticarcillin/clavulanate combinations amongst Escherichia coli isolates have been attributed to an increased frequency of hyperproduction of TEM-1 beta-lactamase. To test this claim we compared the activities of clavulanate combinations against consecutive E. coli isolates producing TEM-1 beta-lactamase that were obtained from clinical material at The London Hospital during 1982 (n = 50) and 1989 (n = 46). Enzyme production was quantified and related to the level of clavulanate required to potentiate amoxycillin and ticarcillin. The levels of TEM-1 enzyme production varied 150-fold amongst the isolates, partly because of variation in the gene copy number. A clear correlation existed between enzyme quantity and levels of resistance to the clavulanate combinations. However, there was no significant difference (P greater than 0.05, Mann-Whitney U test) between the isolates obtained in 1982 and 1989 in terms of the clavulanate concentrations required to potentiate the penicillins, or in the distribution of beta-lactamase activities present.

Amoxicillin↗
PubMed1990

Cloning, localization, and permanent expression of a Drosophila octopamine receptor.

A cDNA for a member of the G protein-coupled receptor family was isolated from Drosophila using a probe derived from a human beta 2-adrenergic receptor cDNA. This Drosophila receptor gene is localized at 99A10-B1 on the right arm of chromosome 3 and is preferentially expressed in Drosophila heads. The insect octopamine receptor has been permanently expressed in mammalian cells, where it mediates the attenuation of adenylate cyclase activity and exhibits a pharmacological profile consistent with an octopamine type 1 receptor. Sequence and pharmacological comparisons indicate that the octopamine receptor is unique but closely related to mammalian adrenergic receptors, perhaps as an evolutionary precursor.

Amino Acid Sequence↗
PubMed1990

Characterization of two classes of opioid binding sites in Drosophila melanogaster head membranes.

Opioid receptors have been characterized in Drosophila neural tissue. [3H]Etorphine (universal opioid ligand) bound stereospecifically, saturably, and with high affinity (KD = 8.8 +/- 1.7 nM; Bmax = 2.3 +/- 0.2 pmol/mg of protein) to Drosophila head membranes. Binding analyses with more specific ligands showed the presence of two distinct opioid sites in this tissue. One site was labeled by [3H]dihydromorphine ([3H]DHM), a mu-selective ligand: KD = 150 +/- 34 nM; Bmax = 3.0 +/- 0.6 pmol/mg of protein. Trypsin or heat treatment (100 degrees C for 15 min) of the Drosophila extract reduced specific [3H]DHM binding by greater than 80%. The rank order of potency of drugs at this site was levorphanol greater than DHM greater than normorphine greater than naloxone much greater than dextrorphan; the mu-specific peptide [D-Ala2,Gly-ol5]-enkephalin and delta-, kappa-, and sigma-ligands were inactive at this site. The other site was labeled by (-)-[3H]ethylketocyclazocine ((-)-[3H]EKC), a kappa-opioid, which bound stereospecifically, saturably, and with relatively high affinity to an apparent single class of receptors (KD = 212 +/- 25 nM; Bmax = 1.9 +/- 0.2 pmol/mg of protein). (-)-[3H]EKC binding could be displaced by kappa-opioids but not by mu-, delta-, or sigma-opioids or by the kappa-peptide dynorphin. Specific binding constituted approximately 70% of total binding at 1 nM and approximately 50% at 800 nM for all three radioligands ([3H]etorphine, [3H]EKC, and [3H]DHM). Specific binding of the delta-ligands [3H][D-Ala2,D-Leu5]-enkephalin and [3H][D-Pen2,D-Pen5]-enkephalin was undetectable in this preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Drosophila melanogaster acetylcholinesterase gene. Structure, evolution and mutations.

Acetylcholinesterase is a key component of cholinergic neurotransmission. In Drosophila melanogaster, acetylcholinesterase is encoded by the Ace locus. We have determined the complete organization of the locus. The transcription unit is 34 kb (1 kb = 10(3) bases) long and encompasses ten exons. We have mapped the 5' end of the transcript, sequenced all the intron/exon boundaries, as well as the 3' end of the transcript. The deduced mature transcript is 4291 nucleotides long without poly(A). Sequencing of the promoter region reveals a potential TATA box and (GA)n motives. The Drosophila coding sequence is more split than its vertebrate counterparts, but the splicing sites of the two last exons are precisely conserved among Drosophila and vertebrate cholinesterases, and intriguingly also with the bovine thyroglobulin gene. Finally, a number of the mutations isolated in earlier genetic work are precisely placed on our molecular map in introns, exons and promoter regions. Among them, for example, a short deletion known to affect acetylcholinesterase level and tissue distribution removes promoter regions and the first non-coding exon.

Acetylcholinesterase↗
PubMed1989

Cloning, sequence analysis and chromosome localization of a Drosophila muscarinic acetylcholine receptor.

Two cDNA clones (3.7 kb and 4.8 kb) encoding a Drosophila muscarinic acetylcholine receptor were isolated from a Drosophila head cDNA library and characterized by automated DNA sequence analysis. The Drosophila muscarinic receptor contains 788 amino acids with a calculated Mr of 84,807 and displays greater than 60% homology with mammalian muscarinic receptors. The muscarinic receptor maps to the tip of the right arm of the second chromosome of the Drosophila genome.

Amino Acid Sequence↗
PubMed1989

Cloning and sequence analysis of the 10 kDa antigen gene of Mycobacterium tuberculosis.

The gene encoding a major protein antigen of Mycobacterium tuberculosis has been cloned and sequenced using oligonucleotide probes derived from the N-terminal sequence of the analogous protein from Mycobacterium bovis BCG. The gene analysis revealed a sequence encoding a protein of 99 amino acid residues, with a molecular mass of 10.7 kDa. Computer prediction suggests that the protein contains three T-cell-determined epitopes (of which one has been demonstrated experimentally) and three B-cell-determined epitopes. The protein sequence was homologous to two prokaryote heat-shock proteins and the gene possessed heat-shock-like promoter sequences upstream of the initiation codon. A hairpin loop identified in the upstream sequence may also be important in regulation of the gene.

Antigens, Bacterial↗
PubMed1987

Enhancer of seizure: a new genetic locus in Drosophila melanogaster defined by interactions with temperature-sensitive paralytic mutations.

Mutations in the enhancer of seizure (e(sei] locus have been isolated on the basis of their ability to cause temperature-induced paralysis of alleles at the seizure (sei) locus at temperatures at which these mutations ordinarily do not paralyze. This enhancer is specific to the seizure locus and is without effect on other temperature-sensitive paralytic mutants including para, nap, tip-E and shi. This suggests that the enhancer responds specifically to the mechanism of paralysis mediated by the seizure mutations. The e(sei) is a recessive mutation which maps to 39.0 on the left arm of chromosome 3. Deficiency mapping has placed it at 69A4-B5 on the salivary gland polytene chromosome map. When a new enhancer allele was isolated following P-M hybrid dysgenesis, there was a concomitant P-element insertion at 69B. In the absence of seizure mutations, the enhancer mutation causes non-temperature dependent hyperactivity when agitated and interferes with the climbing response. Electrophysiological studies examined the effects of increasing temperature on electrical activity in the adult giant fiber/flight muscle system. Neuronal hyperactivity was seen in both e(sei) and sei single mutant homozygotes, but not in wild type. The hyperactivity was more severe in the sei;e(sei) double mutants. The correlation between the physiological effects and the mutant behavior suggests that both sei and e(sei) cause membrane excitability defects. Since previous work has shown that seizure mutants affect [3H]saxitoxin binding to the voltage-sensitive sodium channel, e(sei) may code for a gene product which interacts with this channel.

Alleles↗
PubMed1986

The tip-E mutation of Drosophila decreases saxitoxin binding and interacts with other mutations affecting nerve membrane excitability.

A recessive temperature-sensitive paralytic mutation, tip-E, is associated with reduced binding of [3H]saxitoxin to voltage-sensitive sodium channels in membranes from adult Drosophila heads. There is a decrease of 30-40% in the number of [3H]saxitoxin-binding sites per mg protein (Bmax), but the dissociation constant (Kd) for [3H]saxitoxin binding is normal in the remaining population of binding sites. This decrease is not due to a general hypotrophy of neural tissue since the number of alpha-bungarotoxin binding sites is normal in tip-E mutants. Although saxitoxin binding is reduced in vitro, pharmacological experiments suggest that tip-E mutants have close to the wild-type number of sodium channels in vivo. This suggestion is supported by the observation that at permissive temperatures tip-E only marginally suppresses a mutation which causes enhanced membrane excitability. However, even at permissive temperatures tip-E interacts synergistically with mutations that decrease membrane excitability. In this case, the double mutants exhibit reduced viability and/or longevity. We postulate that either the structure of sodium channels or their microenvironment is altered in tip-E mutants resulting in an increased liability of binding sites in vitro.

Amphibian Proteins↗