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P Taylor

Publications and source records attributed to P Taylor.

At least 361 records · Page 20Linked to original sources
PubMed1991

Role of the peripheral anionic site on acetylcholinesterase: inhibition by substrates and coumarin derivatives.

Propidium has been demonstrated in previous studies to be a selective ligand for the peripheral anionic site on acetylcholinesterase (EC 3.1.1.7). Its association with this site can be advantageously monitored by direct fluorescent titration. We have measured the ability of acetylcholine, acetylthiocholine, haloxon [di-(2-chloroethyl)3-chloro-4-methylcoumarin-7-ylphosphate] , and a coumarin derivative (3-chloro-7-hydroxy-4-methylcoumarin) to dissociate propidium from the peripheral anionic site of Torpedo californica acetylcholinesterase. Measurements were made by back-titration of propidium after complete inhibition of the active center with diisopropylfluorophosphate. Both acetylcholine and acetylthiocholine show substrate inhibition at high substrate concentrations. The concentrations required for occupation of the peripheral site, as ascertained by competition with propidium, correlated well with the concentration dependence for the kinetics of substrate inhibition. These observations are consistent with substrate inhibition being due to binding of acetylcholine or acetylthiocholine at a peripheral anionic site. Displacement of propidium by haloxon and coumarin indicated that these inhibitors also bind to the peripheral anionic site. The dissociation constants ascertained from peripheral site occupation are in agreement with the constants obtained from inhibition kinetics. Evidence is presented that competition with propidium obtained by direct fluorescence titrations, when combined with inhibition kinetics, provides a more reliable means for ascertaining site selectivity of various inhibitors than does a kinetic analysis alone.

Acetylcholine↗
PubMed1991

Clinical diagnosis of malaria: can we improve?

Most cases of malaria in Zimbabwe are diagnosed on the basis of clinical suspicion, without laboratory tests. Of patients treated, between 10 and 30% have malaria parasites on blood slide examination. Can diagnosis be improved by a systematic history? We examined this question in 287 patients treated for malaria in an area of year-round transmission in Zimbabwe. The most common complaints were 'headache' (85.7%), 'bodily weakness' (79.0%) and 'fever/feeling hot' (73.2%). Eighty patients (28%) had malaria parasites on blood smear. Using the blood slide as the standard, we calculated the sensitivity, specificity and positive predictive value of a variety of clinical symptoms and signs. None had a positive predictive value substantially higher than the unknown diagnostic criteria used by health workers (28%). Multivariate analysis showed that 15 different demographic and clinical variables did not significantly predict a positive blood slide result. We conclude that, in this setting, clinical history alone will not improve the diagnosis of malaria.

Chloroquine↗
PubMed1990

Biosynthesis of Torpedo acetylcholinesterase in mammalian cells. Functional expression and mutagenesis of the glycophospholipid-anchored form.

The catalytic subunits of asymmetric and hydrophobic forms of acetylcholinesterase arise from a single gene by alternative mRNA splicing. Each protein is encoded in three exons, with exons 1 and 2 encoding sequence common to both forms and exons 3A and 3H specifying unique carboxyl-terminal domains. We examined the expression of cDNAs for the two forms by transient transfection in COS-1 cells. The catalytic subunit of the asymmetric form expressed by transfected cells exhibits low activity and is retained within the cell. The cDNA encoding hydrophobic acetylcholinesterase directs the synthesis of enzyme with much greater activity, which is expressed on the outer surface of the cell membrane and can be released by phosphatidylinositol-specific phospholipase C. A mutant truncated acetylcholinesterase which lacks either carboxyl-terminal sequence encoded by the alternative exons is secreted into the medium. An exon 1-3H fusion mutant, created by deletion of coding exon 2 from the hydrophobic form cDNA, is glycophospholipid-linked. The 30-amino acid carboxyl-terminal domain specified by exon 3H appears necessary and sufficient to direct glycophospholipid attachment. Thus, heterologous expression of wild-type and mutant acetylcholinesterase proteins indicates that the carboxyl-terminal domains specified by alternative coding exons determine the cellular dispositions of acetylcholinesterase.

Acetylcholinesterase↗
PubMed1990

Structure of the thromboxane receptor antagonist EP 092.

7-(3-[1-(4-Phenylthiosemicarbazono)ethyl]-bicyclo[2.2.1]hept-2- yl)-5-heptenoic acid, C23H31N3-O2S, Mr = 413.7, monoclinic, P2(1)/a, a = 12.9650 (7), b = 11.2081 (6), c = 16.8941 (12) A, beta = 110.452 (5) degrees, V = 2300.2 A3, Z = 4, Dx = 1.194 g cm-3, Mo K alpha, lambda = 0.71073 A, mu = 1.55 cm-1, F(000) = 888, T = 298 K. Final R = 0.0472 with 2778 independent data. EP 092 is a thromboxane receptor antagonist akin to many other analogues of the thromboxane A2 [Wilson & Jones (1985). Adv. Prostaglandin Thromboxane Leukotriene Res. 14, 393-425].

Molecular Conformation↗
PubMed1990

Interaction of an organophosphate with a peripheral site on acetylcholinesterase.

O-Ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (MPT) is an active site directed inhibitor of acetylcholinesterase (AChE). Inhibition of the Electrophorus electricus (G4) enzyme follows classical second-order kinetics. However, inhibition of total mouse skeletal muscle AChE and inhibition of the individual molecular forms from muscle, including the monomeric species, do not proceed as simple irreversible bimolecular reactions. Similarly, complex inhibition kinetics are observed for the purified enzyme from Torpedo californica. AChE can be cross-linked with glutaraldehyde into a semisolid matrix. Under these conditions the abnormal concentration dependence for MPT inhibition is accentuated, and a range of MPT concentrations can be found where inhibition of polymerized AChE is far less than that observed at lower concentrations. Inhibition in certain concentration ranges is partially reversible after removal of all unbound ligand. Thus, there are two different modes of organophosphorus inhibition by MPT: the classical irreversible phosphorylation of the active site and a reversible interaction at a site peripheral to the active center. Propidium, a well-studied peripheral site ligand, can prevent the later interaction. Hence, the second site of MPT interaction with AChE may overlap or be linked to the peripheral anionic site of AChE characterized by the binding of propidium and other peripheral site inhibitors.

Animals↗
PubMed1990

Evaluation of the reagent strip test for haematuria in the control of Schistosoma haematobium infection in schoolchildren.

Several recent reports have indicated the potential of the reagent strip test for haematuria in the diagnosis of Schistosoma haematobium infection. Approximately 15,000 schoolchildren from a population of 40,000 people were examined for reagent strip microhaematuria on three occasions between 1986 and 1987 and treated with praziquantel 40 mg/kg if positive. The reagent strip was evaluated against a single filtration of 10 ml urine for S. haematobium eggs. Initially 65.9% of children were treated followed by 37.5% at the second examination 6 months later and 44.5% at the third examination a further 12 months later. Reagent strip sensitivity was shown to be related to the intensity of infection. The reagent strip specificity improved significantly with successive treatments indicating that haematuria was more sensitive than parasitology for light infections. The amount of S. haematobium reinfection was highest in the 7-9 year olds decreasing to the 16-20 year age group which suggested an impact of protective immunity. It was concluded that microhaematuria is a valuable indicator for the diagnosis of S. haematobium in national control programmes and can be substituted for parasitological examination with advantage but sensitivity and specificity should continue to be evaluated throughout the programme.

Adolescent↗
PubMed1990

Reduction of complement activation during bypass by prime manipulation.

Complement activation is believed to be of importance in the development of complications arising after cardiopulmonary bypass. The effect on complement activation of priming the extracorporeal circuit with crystalloid alone, crystalloid plus albumin, or crystalloid plus the plasma expander polygeline was assessed in 36 patients undergoing coronary artery operations with cardiopulmonary bypass using a bubble oxygenator. Activation of the alternative and common complement pathways was monitored before, during, and after the bypass period by measuring concentrations of factor B and its fragment Ba and C3 and its fragment C3d. Complement activation occurred in all three groups of patients, with no difference between the crystalloid and crystalloid-albumin groups. In contrast, Ba fragment concentrations were persistently and significantly lower during and after bypass in the polygeline group, denoting reduced complement activation. C3d levels also showed a tendency to be lower in this group. Our results indicate that addition of polygeline to the priming solution reduces complement activation. Because complement activation is associated with morbidity after cardiopulmonary bypass, addition of polygeline to the priming solution may offer an inexpensive method of reducing morbidity after cardiopulmonary bypass.

Albumins↗
PubMed1990

Isotretinoin-basal cell carcinoma prevention trial. Design, recruitment results, and baseline characteristics of the trial participants. The ISO-BCC Study Group.

The Isotretinoin-Basal Cell Carcinoma Prevention Trial (ISO-BCC Study) is a double-masked, randomized, placebo controlled, multicenter clinical trial. It is the first intramural cancer chemoprevention trial sponsored by the Division of Cancer Prevention and Control of the National Cancer Institute. This trial was designed to evaluate the effectiveness of chronic administration of low dosage levels (10 mg) of a synthetic retinoid, isotretinoin, in reducing the incidence of basal cell carcinoma in a high-risk population and to determine the incidence and severity of side effects associated with this long-term treatment. Between 1984 and 1987, eight clinical centers enrolled 981 participants between the ages of 40 and 75, who had two or more biopsy proven basal cell carcinomas in the 5 years before trial entry. This article describes the trial design, recruitment results, and baseline characteristics of the participant population in the ISO-BCC Study.

Adult↗
PubMed1990

The rational use of antischistosomal drugs in schistosomiasis control.

The paper examines the available antischistosomal drugs in Zimbabwe and the use of population-based chemotherapy as an effective strategy of morbidity reduction in schistosomiasis control. The problems of poor drug efficacy and side-effects that were associated with earlier antischistosomal drugs have largely been overcome with the advent of recent, safe and effective oral drugs. The main constraints of population-based chemotherapy are the costs of drug procurement, transport and the logistics of delivery. In highly endemic areas, screening for infection may not be necessary and following pilot surveys mass chemotherapy can be carried out. Nevertheless, anecdotal and unverified reports suggest that mass chemotherapy may result in lightly infected individuals losing their residual immunity and risk heavy reinfection. To lower costs of the drugs and reduce organizational problems of delivery it may be preferable to target treatment at high risk groups. These groups include certain age classes with peak prevalence and intensity of infection and those predisposed to get heavy infections. Treatment prevents the development of overt disease in these high risk groups and also significantly reduces contamination and consequently transmission. However, chemotherapy only results in temporary relief and its impact requires to be sustained by parallel and long-lasting interventions that include improved sanitation, better water supplies and health education. Suggestions are made on how to train and utilize community and public health workers for such control programmes.

Drug Therapy, Combination↗
PubMed1990

Single gene encodes glycophospholipid-anchored and asymmetric acetylcholinesterase forms: alternative coding exons contain inverted repeat sequences.

Polymorphic forms of acetylcholinesterase are tethered extracellularly either as dimers membrane-anchored by a glycophospholipid or as catalytic subunits disulfidelinked to a collagen tail that associates with the basal lamina. Genomic clones of acetylcholinesterase from T. californica revealed that individual enzyme forms are encoded within a single gene that yields multiple mRNAs. Each enzyme form is encoded in three exons: the first two exons, bases -22 to 1502 and 1503 to 1669, encode sequence common to both forms, while alternative third exons encode a hydrophobic C-terminal region, to which a glycophospholipid is added upon processing, and a nonprocessed C-terminus, yielding a catalytic subunit that disulfide-links with a collagen-like structural unit. The 3' untranslated region of each alternative exon contains tandem repeat sequences that are inverted with respect to the other exon. This may either dictate alternative exon usage by formation of cis stem-loops or affect the abundance of translatable mRNA by trans-hybridization between the alternative spliced mRNA species.

Acetylcholinesterase↗
PubMed1990

Molecular cloning of mouse acetylcholinesterase: tissue distribution of alternatively spliced mRNA species.

We have isolated cDNA clones encoding acetylcholinesterase from mouse muscle and brain. The polymerase chain reaction was used to amplify cDNA clones from C2 myotubes encoding the entire open reading frame and large segments of the 5' and 3' untranslated regions. The muscle cDNA clones were used to isolate clones from a brain library encoding the same mRNA species. The mouse clones encode a catalytic subunit containing a C-terminal sequence similar to that of the hydrophilic species of Torpedo. The mouse acetylcholinesterase sequence shares approximately 88% and 61% amino acid identity with bovine and Torpedo acetylcholinesterases, respectively, but only 52% identity with mouse butyrylcholinesterase, the sequence of which we have also deduced by molecular cloning. Northern blot and RNAase protection analyses indicate that the cDNA clones were derived from the acetylcholinesterase transcript that predominates in most expressing tissues. In contrast, erythroid cells are enriched in an mRNA species whose sequence diverges from that of the cDNA in the region encoding the C-terminus of the enzyme.

Acetylcholinesterase↗
PubMed1990

Complement activation before, during and after cardiopulmonary bypass.

Plasma levels of the complement parent molecules C3, C4, and factor B and their split products, C3d, C4d, and Ba were measured in 12 patients undergoing cardiopulmonary bypass for coronary artery surgery. Alternative and common complement pathway activation, demonstrated by statistically significant rising levels of Ba (P less than 0.05), and C3d (P less than 0.05) and by elevated Ba:B (P less than 0.05) and C3d:C3 (P less than 0.05) ratios were found before the institution of cardiopulmonary bypass but following heparin administration suggesting that heparin may itself initiate alternative pathway activation. In addition, significant depletion of parent complement components and elevation of split product concentrations was seen during bypass suggesting classical and alternate pathway activation (P less than 0.01). This study clarifies the pathways of complement activation during bypass and presents evidence that heparin administration may initially activate the complement cascade.

Cardiopulmonary Bypass↗
PubMed1990

Molecular basis for dominantly inherited inclusion body beta-thalassemia.

Analysis of the molecular basis of dominantly inherited beta-thalassemia in four families has revealed different mutations involving exon 3 of the beta-globin gene. It is suggested that the phenotypic difference between this condition and the more common recessive forms of beta-thalassemia lies mainly in the length and stability of the abnormal translation products that are synthesized and, in particular, whether they are capable of binding heme and producing aggregations that are relatively resistant to proteolytic degradation.

Amino Acid Sequence↗
PubMed1990

Mutagenesis of essential functional residues in acetylcholinesterase.

The cholinesterases are serine hydrolases that show no global similarities in sequence with either the trypsin or the subtilisin family of serine proteases. The cholinesterase superfamily includes several esterases with distinct functions and other proteins devoid of the catalytic serine and known esterase activity. To identify the residues involved in catalysis and conferring specificity on the enzyme, we have expressed wild-type Torpedo acetylcholinesterase (EC 3.1.1.7) and several site-directed mutants in a heterologous system. Mutation of serine-200 to cysteine results in diminished activity, while its mutation to valine abolishes detectable activity. Two conserved histidines can be identified at positions 425 and 440 in the cholinesterase family; glutamine replacement at position 440 eliminates activity whereas the mutation at 425 reduces activity only slightly. The assignment of the catalytic histidine to position 440 defines a rank ordering of catalytic residues in cholinesterases distinct from trypsin and subtilisin and suggests a convergence of a catalytic triad to form a third, distinct family of serine hydrolases. Mutation of glutamate-199 to glutamine yields an enzyme with a higher Km and without the substrate-inhibition behavior characteristic of acetylcholinesterase. Hence, modification of the acidic amino acid adjacent to the serine influences substrate association and the capacity of a second substrate molecule to affect catalysis.

Acetylcholinesterase↗