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Biomedical subjects

M Longstaff

Publications and source records attributed to M Longstaff.

At least 19 recordsLinked to original sources
PubMed2001

Response-time dynamics: evidence for linear and low-dimensional nonlinear structure in human choice sequences.

Response time (RT) is a commonly used measure of cognitive performance, which is usually characterized as stochastic. However, useful information may be hidden in the apparently random fluctuations of RT. Dynamical systems analysis techniques allow an exploration of the alternative hypothesis that RT fluctuations are deterministic, albeit in a complex manner. We applied careful task construction and noise-reduction and surrogate series tests to show that RT series from a forced-pace serial response-time task have low-dimensional chaotic characteristics. In Experiment 1, 80% of subjects' filtered RT series had low dimensionality, sensitive dependence on initial conditions, spectra close to 1/f, and stable attractor geometry across sessions. In Experiment 2, we showed that the size of the inter-stimulus interval (ISI) determined the number of subjects with low-dimensional chaotic series. A small ISI caused 100% of subjects to respond in the chaotic regime, whereas only 25% had a low-dimensional chaotic RT component when the ISI was large. We argue that demanding task requirements cause a reduction in the dimensionality of the dynamics, producing RT fluctuations that may reflect a response strategy for controlling RT.

Adult↗
PubMed2000

Detecting nonlinearity in psychological data: techniques and applications.

Modern graphical and computational techniques for detecting nonlinearity in psychological data sets are presented. These procedures allow researchers to determine the information complexity of temporal data, using physiological and psychological measurements, and to provide evidence for chaos in time series contaminated by measurement noise. Problems with noise reduction and appropriate experimental control, using surrogate time series, are discussed, and applications of the technology are illustrated, using response time, handwriting, and typing data sets. In an experimental application of appropriate nonlinear analysis procedures, the results of a time series prediction experiment confirm that some subjects are sensitive to chaos. In contrast to previous attempts demonstrating sensitivity to chaos, the experiment reported here employs surrogate series to control for linear stochastic aspects of the stimulus sequences, such as autocorrelation. Recommendations for the selection of appropriate software for performing nonlinear analyses are presented, including a comprehensive list of World-Wide Web sites offering such software.

Behavioral Sciences↗
PubMed1999

Immunogenicity of peptides derived from a fibronectin-binding protein of S. aureus expressed on two different plant viruses.

The D2 peptide derived from an S. aureus fibronectin-binding protein (FnBP) was expressed on the surface of the icosahedral cowpea mosaic virus (amino acids 1-30 of D2) or on the rod-shaped potato virus X (amino acids 1-38 of D2), termed CPMV-MAST1 and PVX-MAST8, respectively. Mice and rats were immunized subcutaneously with CPMV-MAST1 and mice with PVX-MAST8 in adjuvant and high titres of FnBP-specific antibody were obtained. The mouse IgG was predominantly of the IgG2a and IgG2b isotypes, which strongly bound complement component C1q, suggesting a TH1-bias in the peptide-specific responses. Sera from mice and rats immunized with CPMV-MAST1 and from mice immunized with PVX-MAST8 were shown to completely inhibit the binding of fibronectin to immobilised recombinant FnBP and rat sera against CPMV-MAST1 were able to block adherence of S. aureus to fibronectin. These studies demonstrate that the D2 peptide is highly immunogenic when expressed on 2 different plant viruses and highlight the potential of plant virus-based vaccines to protect against S. aureus infections.

Adhesins, Bacterial↗
PubMed1998

Binding characteristics of anti-atrazine monoclonal antibodies and their fragments synthesised in bacteria and plants.

Single-chain antibody fragments (scAb), specific for the herbicide atrazine, have been expressed in the bacterium Escherichia coli and in transgenic tobacco plants. The scAb could be purified as a monomer (monovalent) via a hexa-histidine tail or as a dimer (divalent) by antibody affinity chromatography. In competition ELISA, the bacterial scAb showed the same specificity for atrazine and related triazine herbicides as the parental mAb cell line, but both plant and bacterial monomeric scAbs showed increased sensitivity to free atrazine. Surface plasmon resonance (BIAcore 2000) analysis confirmed that purified scAb, derived from plant or bacteria, retained similar association rates as the mAb. However, the monomeric plant and bacterial scAbs showed a lower affinity for immobilised antigen, than the equivalent dimeric scAbs or mAb. This decrease in affinity was due to a 10 fold slower dissociation rate and is likely due to loss of the avidity contribution of dimeric molecules.

Antibodies, Monoclonal↗
PubMed1998

Expression and characterisation of single-chain antibody fragments produced in transgenic plants against the organic herbicides atrazine and paraquat.

Single-chain antibody fragments (scAbs), which have a human C-kappa constant domain and a hexa-histidine tail attached to the carboxy terminus of the single-chain Fv (ScFv) fragments to facilitate purification, have been raised against the herbicides paraquat and atrazine and expressed in transgenic Nicotiana tabacum cv. Samsun NN. Prior to purification, the anti-atrazine scAb is expressed as up to 0.014% of soluble leaf protein and has a binding profile in ELISA, against an atrazine-bovine serum albumin (BSA) conjugate, similar to that of the scAb produced in Escherichia coli. Competition ELISA has shown that the plant-derived scAb also recognises free atrazine. Following antibody affinity purification to isolate dimers, the affinity for immobilised antigen approaches that of the parental monoclonal antibody. This was confirmed by surface plasmon resonance analysis. The purified scAb also recognises related triazine herbicides. When isolated from cell-suspension cultures, the anti-paraquat scAb binds to a paraquat conjugate in a concentration-dependent manner, with a profile similar to the parental monoclonal antibody. This is the first demonstration that functional scAbs against organic pollutants can be produced in transgenic plants and that the scAbs may be appropriate for the development of immunoassay-based detection systems.

Atrazine↗
PubMed1998

Production and purification of active snowdrop lectin in Escherichia coli.

Recombinant snowdrop lectin was produced in Escherichia coli from a cDNA clone encoding mature Galanthus nivalis agglutinin. After induction with isopropylthio-beta-D-galactoside, inclusion bodies from E. coli were solubilised and the G. nivalis agglutinin purified by metal-affinity chromatography using a carboxy-terminal hexahistidine tag. The protein was refolded on the metal-affinity column prior to elution. After purification, the recombinant G. nivalis agglutinin agglutinated rabbit erythrocytes to a dilution similar to that determined for 'native' lectin purified from snowdrop, and showed similar specific binding to mannose. The toxicity of the recombinant G. nivalis agglutinin towards rice brown planthopper (Nilaparvata lugens) was shown to be similar to that of 'native' G. nivalis agglutinin when incorporated into an artificial diet. The recombinant G. nivalis agglutinin is thus functionally similar to 'native' snowdrop lectin.

Amino Acid Sequence↗
PubMed1993

Extreme resistance to potato virus X infection in plants expressing a modified component of the putative viral replicase.

Three types of mutation were introduced into the sequence encoding the GDD motif of the putative replicase component of potato virus X (PVX). All three mutations rendered the viral genome completely noninfectious when inoculated into Nicotiana clevelandii or into protoplasts of Nicotiana tabacum (cv. Samsun NN). In order to test whether these negative mutations could inactivate the viral genome in trans, the mutant genes were expressed in transformed N.tabacum (cv. Samsun NN) under control of the 35S RNA promoter of cauliflower mosaic virus and the transformed lines were inoculated with PVX. In 10 lines tested in which the GDD motif was expressed as GAD or GED there was no effect on susceptibility to PVX. In two of four lines transformed to express the ADD form of the conserved motif, the F1 and F2 progeny plants were highly resistant to infection by PVX, although only to strains closely related to the source of the transgene. The resistance was associated with suppression of PVX accumulation in the inoculated and systemic leaves and in protoplasts of the transformed plants, although some low level viral RNA production was observed in the inoculated but not the systemic leaves when the inoculum was as high as 100 or 250 micrograms/ml PVX RNA. These results suggest for a plant virus, as reported previously for Q beta phage, that virus resistance may be engineered by expression of dominant negative mutant forms of viral genes in transformed cells.

Amino Acid Sequence↗
PubMed1992

The effect of proanthocyanidin-rich hulls and proanthocyanidin extracts from bean (Vicia faba L.) hulls on nutrient digestibility and digestive enzyme activities in young chicks.

Proanthocyanidins were prepared from three bean (Vicia faba L.) varieties by extracting hulls in aqueous acetone. The amounts of freeze-dried extracts recovered were 74, 89 and 97 g/kg hull for the varieties Brunette, Statissa and Minica respectively. Chicks (3 weeks old) were fed on a maize-soya-bean control diet or the same control diet substituted with either 30 g proanthocyanidin extracts/kg or 300 g proanthocyanidin-rich hulls/kg. Chicks were tube-fed diets twice daily for 4 d. Nutrient digestibilities were calculated from amounts present in diets and freeze-dried excreta with the aid of titanium dioxide as a marker. Enzyme activities were measured in digesta removed from the jejunum. Extracts of proanthocyanidins depressed the digestibility of protein by 34%, starch by 3% and had no effect on the digestibility of lipid. Proanthocyanidin-rich hulls depressed the digestibility of protein by 62%, starch by 6% and lipid by 4%. Digestive enzyme activities were depressed to the same extent by extracts and hulls, trypsin (EC 3.4.21.4) by 55 and 62%, alpha-amylase (EC 3.2.1.1) by 75 and 78% and lipase (EC 3.1.1.3) by 31 and 32% for proanthocyanidin-extract and proanthocyanidin-rich-hull diets respectively. The susceptibility of substrates as well as enzymes to the effects of proanthocyanidins is discussed.

Animals↗
PubMed1991

The inhibitory effects of hull polysaccharides and tannins of field beans (Vicia faba L.) on the digestion of amino acids, starch and lipid and on digestive enzyme activities in young chicks.

The effects of polysaccharides and tannins present in the hulls of field beans (Vicia faba L.) on the digestion of amino acids, starch and lipid were studied in poultry. A control diet without hulls and the same diet substituted with 400 g hulls/kg diet from three different varieties of beans were fed to 3-week-old chicks for 4 d. Digestibility coefficients for amino acids, starch and lipid were calculated from measurements made of these nutrients in the diets and the freeze-dried excreta with the aid of titanium dioxide as a marker. Activities of trypsin (EC 3.4.21.4), alpha-amylase (EC 3.2.1.1), and lipase (EC 3.1.1.3) in digesta removed from the upper jejunum, sucrase (EC 3.2.1.48) in the gut mucosa from the upper jejunum, and alpha-amylase and lipase in the pancreas were measured. The hulls were analysed for their polysaccharide and tannin contents. Results showed that the hulls were mostly carbohydrate in composition, with cellulose the predominant polysaccharide. Tannins present in the hulls of two coloured-flowering varieties (Brunette and Minica) were of the condensed type. The diet with tannin-free hulls (white-flowering variety Medes) lowered slightly the digestion of amino acids, starch and lipid compared with the control diet. This effect was believed to be due to inhibition of digestive enzymes, possibly through their adsorption onto the hulls. Diets with tannin-rich hulls (varieties Brunette and Minica) caused a large reduction in the digestion of amino acids, starch and lipid compared with the control diet mainly due to inactivation of digestive enzymes by the formation of tannin-enzyme complexes in the digestive tract. Enzyme activities could be partially restored by the addition of polyvinylpyrrolidone to the digesta. Tannins inactivated trypsin the most, alpha-amylase to a lesser extent and lipase the least and as a consequence lowered the digestion of amino acids the most, starch to a lesser extent and lipid the least. Tannins did not induce an increased pancreatic production of digestive enzymes, nor did they affect activity of jejunum mucosal sucrase. Condensed tannins from Brunette and Minica hulls were partially extractable in methanol alone, but required acidic methanol for fuller extraction. The vanillin:anthocyanidin ratio suggested that tannins were polymerized to the same degree in the Brunette and Minica varieties, both in the methanol and acidic methanol extracts. Hulls from the variety Minica contained a greater amount of methanol-extractable tannins, the quantity of remaining tannins that required acidic methanol for extraction being the same for both varieties.

Amino Acids↗
PubMed1990

Cucumber mosaic virus satellite RNA (Y strain): analysis of sequences which affect yellow mosaic symptoms on tobacco.

Plants infected with cucumber mosaic virus (CMV) (KIN strain) produce a mild mosaic disease on tobacco whereas infections of CMV with satellite RNA (strain Y) cause a severe yellow mosaic. Analysis of recombinant and mutant forms of satellite RNA identified a site (nucleotides 185/186) in the Y satellite RNA that affects the ability to induce the yellow mosaic in combination with CMV but not with tomato aspermy virus. The location of this site with respect to other mutations in the satellite RNA indicated that polypeptides, which may be encoded by the satellite RNA, have no role in induction of yellow mosaic symptoms. The symptom induction is therefore an effect of the satellite RNA on the host plant with the intervention of the helper virus. In the course of the mutation analysis of satellite RNA we detected several secondary mutations which arose in planta. Two of these were deletions of more than 80 nucleotides. Other forms of mutant satellite RNA were non-functional even though the modifications involved nucleotides completely within the large secondary deletions. These data imply complex intramolecular interactions in the satellite RNA.

Base Sequence↗
PubMed1989

Wheat phosphoglycerate kinase: evidence for recombination between the genes for the chloroplastic and cytosolic enzymes.

We have isolated and sequenced cDNA clones containing the entire coding region of both the chloroplast and cytosolic versions of phosphoglycerate kinase from wheat. Comparison of these sequences reveals a higher than expected level of similarity between the nucleic acids and encoded proteins. Analysis of this data in relation to that for phosphoglycerate kinase sequences of mammals, prokaryotes and yeasts suggests that the wheat genes have recombined. This has resulted in the chloroplast and cytosolic kinases being more similar to each other than would be expected if the chloroplast enzyme had evolved directly from that of a prokaryotic progenitor.

Amino Acid Sequence↗
PubMed1989

Digestion of fibre polysaccharides of pea (Pisum sativum) hulls, carrot and cabbage by adult cockerels.

Characterization of the carbohydrates of pea (Pisum sativum) hulls, carrot and cabbage using both colorimetric and gas-liquid chromatographic techniques permitted a detailed investigation into the extent of digestion of differing types of fibre. These digestion studies were greatly aided by the development of a rapid bioassay employing starved adult cockerels. Total collection of undigested residues, uncontaminated by food spillage, could be made from trays placed under the cockerels. Chemical analysis showed that pea hulls consisted mainly of fibre with very little available carbohydrate present, whereas more than half of freeze-dried carrot and cabbage consisted of available carbohydrate (sucrose, glucose, fructose, starch) and consequently considerably less fibre was present. The fibre of carrot and cabbage was similarly composed of nearly equal amounts of neutral and acidic polysaccharides, whereas pea-hull fibre had four times as much neutral as acidic polysaccharides. The digestibility of total neutral polysaccharides from all three foodstuffs was extremely low. However, there appeared to be preferential digestion of polysaccharides composed of rhamnose, arabinose and galactose residues, all associated with pectic material, in contrast to the indigestibility of polysaccharides composed of fucose, xylose and glucose. Acidic polysaccharides were digested to a greater extent than neutral ones, and those of carrot and cabbage more so than pea hulls. The polysaccharides which were the most soluble were also the most digestible, but due to the arbitrariness of polysaccharide solubility, quantification of their total digestibility per se was considered not possible.

Animals↗
PubMed1989

Complete coding sequence of wheat phosphoribulokinase: developmental and light-dependent expression of the mRNA.

We have isolated and sequenced a cDNA clone which contains the entire coding sequence of the precursor to a subunit of wheat phosphoribulokinase (PRKase). (The enzyme is a homodimer). The cDNA contains 1533 bp and has an open reading frame of 1212 nucleotides. This encodes a protein with an amino-terminal transit sequence of 53 amino acids, while the part that forms the mature protein contains 351 amino acids and has a molecular weight of 39,200 daltons. A comparison of the wheat amino acid sequence with that already known for the mature protein of spinach reveals that there are identical residues in 86% of the positions but their transit peptides differ substantially from one another. The mature wheat and spinach proteins are identical in a segment of over 50 amino acids near the amino-terminus which is the region believed to be involved in ATP binding and in regulation by light of the catalytic activity of the enzyme. We further demonstrate that the expression of PRKase mRNA in wheat leaves is regulated in a developmental, tissue-specific and light dependent manner. We also show that the light-induced increase in the steady-state levels of this mRNA is dependent on the developmental stage of the leaf.

Amino Acid Sequence↗
PubMed1988

Chloroplast fructose-1,6-bisphosphatase: the product of a mosaic gene.

We show here that light stimulates the expression of nuclear genes in wheat leaves for chloroplast fructose-1,6-bisphosphatase (FBPase) and describe a sequence of amino acids in this enzyme which may be responsible, via thioredoxin, for the light regulation of its activity. This data results from (a) our isolation and characterization of a cDNA of this enzyme which contains its entire coding sequence, and (b) our use of this cDNA as a probe to detect mRNA levels in wheat plants subjected to different light regimes. The similarity in amino acid sequence of the encoded enzyme from diverse sources suggests that the FBPase genes all had a common origin. However, their control sequences have been adjusted so that they are appropriately expressed and their coding sequences modified so that the enzymic activity of their products are suitably regulated in the particular cellular environment in which they must function. The light-activated regulatory sequences in the gene for the chloroplast protein have probably come together by a shuffling of DNA segments.

Amino Acid Sequence↗
PubMed1987

Digestion of starch and fibre carbohydrates in peas by adult cockerels.

The digestion of starch and fibre by adult cockerels fed peas which were whole, ground, autoclaved, heated, dehulled, cooked or supplemented with a cellulose degrading enzyme was studied. The starch in ground peas that had been autoclaved, heated or dehulled was slightly, though not significantly, better digested than the starch in peas that had been ground only. Feeding peas whole greatly reduced starch digestibility. Cooking failed to improve starch digestibility as retrograded starch produced in the cooking process was not digested. The more finely ground the foodstuff, the better the in vitro enzymatic hydrolysis of starch. Starch digestibility correlated well (r2 = 0.80) with the true metabolisable energy values obtained for the different pea treatments. In experiment 1 cockerels digested on average 0.22 of the pea fibre from the different forms of peas. A significant decrease in xylose digestion was observed when birds were fed dehulled peas, birds excreting more xylose than they ingested. In experiment 2, cockerels digested on average 0.38 of the pea fibre from different forms of peas. A reduction in fibre digestion was observed when birds were fed cooked peas as a consequence of a decreased digestibility of all monosaccharide residues. A slight increase in fibre digestion was observed when peas were augmented with 'cellulase', entirely because of an increase in xylose digestion.

Animals↗
PubMed1986

The sequence of carnation etched ring virus DNA: comparison with cauliflower mosaic virus and retroviruses.

Carnation etched ring virus (CERV) DNA comprises 7932 bp. CERV primer binding sites and overall genome organization are similar to those of the related cauliflower mosaic virus (CaMV). The six open reading frames of CERV showed amino acid homology (50-80%) with CaMV ORFs I-VI; no homologues of CaMV ORFs VII or VIII were found. CERV ORFs 1-5 interface each other with the sequence ATGA. The comparison of CERV ORF5 with CaMV ORFV highlighted regions which show homologies to retrovirus gag/pol protease, RNase H and DNA polymerase domains; the possibility that the DNA polymerase domain comprises two subdomains, operating off different templates, is discussed. Both CERV and CaMV ORFs I have sequence homology to tobacco mosaic virus P30 and plastocyanin.

Journal Article↗