Showing papers by "University of Glasgow published in 1984"
TL;DR: It is suggested that proteins and other biological macromolecules may have evolved to take functional advantage not only of mean conformational states but also of the inevitable thermal fluctuations about the mean.
Abstract: A general model is presented whereby lignand-induced changes in protein dynamics could produce allosteric communication between distinct binding sites, even in the absence of a macromolecular conformational change. Theoretical analysis, based on the statistical thermodynamics of ligand binding, shows that cooperative interaction free energies amounting to several kJ · mol-1 may be generated by this means. The effect arises out of the possible changes in frequencies and amplitudes of macromolecular thermal fluctuations in response to ligand attachment, and can involve all forms of dynamic behaviour, ranging from highly correlated, low-frequency normal mode vibrations to random local anharmonic motions of individual atoms or groups. Dynamic allostery of this form is primarily an entropy effect, and we derive approximate expressions which might allow the magnitude of the interaction in real systems to be calculated directly from experimental observations such as changes in normal mode frequencies and mean-square atomic displacements. Long-range influence of kinetic processes at different sites might also be mediated by a similar mechanism. We suggest that proteins and other biological macromolecules may have evolved to take functional advantage not only of mean conformational states but also of the inevitable thermal fluctuations about the mean.
642 citations
TL;DR: The structural characterization of pectins and the gels which they form, in relation to auxin-induced extension growth, the ripening of fruit, and cellular recognition are discussed in this article.
Abstract: This review deals with recent advances in the structural characterization of pectins and the gels which they form, in relation to auxin-induced extension growth, the ripening of fruit, and cellular recognition. Pectins are block polysaccharides. Heavily branched, largely methyl-esterified blocks alternate with unbranched blocks of varying degrees of esterification. The unbranched, non-esterified blocks can aggregate through calcium binding to form the junction zones that hold a gel together. The aggregates are of two, or possibly four, chains at low calcium levels, and larger with excess calcium. The fall in wall pH during auxin-induced growth activates glycanase enzymes. These may attack some components of the pectic fraction, as well as xyloglucans. Pectin-bound calcium ions may be displaced but this probably has little effect on gel strength. Pectins may be cross-linked by diferulate esters when growth stops. The softening of ripe fruit is due to loss of cohesion in the pectin gel. In apples this results from replacement of the pectins by more esterified forms. In many other fruits it results from depolymerization by polygalacturonases, assisted by pectinesterases, so that the remaining segments are too short for effective calcium binding. Pectins have a further role in the recognition reactions between plant cells and some of their bacterial and fungal pathogens.
573 citations
TL;DR: Localized monomerizing and stability determinants of CoIE1 are localized to within a 0.38 kb region that, when cloned into plasmid vectors, greatly increases their stability.
462 citations
TL;DR: Maternal age specific rates for all major chromosome aberrations have been determined and it is postulated that a maternal age effect acting particularly on first meiotic nondisjunction leads to a higher spontaneous abortion rate with advancing maternal age for aneuploid as compared to euploid conceptions.
Abstract: Maternal age specific rates for all major chromosome aberrations have been determined in 52 965 pregnancies in mothers 35 years of age and over at the time of amniocentesis. Rates increase exponentially with advancing maternal age for trisomies 21, 18 and 13, and for the XXX and XXY syndromes, but in the autosomal trisomies this rise appears to be followed by a levelling off at the upper end of the age range. A significant inverse relationship with maternal age is found for 45,X cases. It is postulated that these various patterns are the result of the interaction of three principal factors: a maternal age effect acting particularly on first meiotic nondisjunction: a higher spontaneous abortion rate with advancing maternal age for aneuploid as compared to euploid conceptions; and an increased probability of spontaneous abortion before the time of amniocentesis for conceptions with more extensive chromosome imbalance. A stepwise logistic regression analysis of 13 299 pregnancies in which both parental ages are known shows that the father's age does not influence these maternal age specific rates, with the possible exception of the 47,XXY syndrome.
391 citations
TL;DR: The action of cholinergic neurons in the graft onto elements in the host hippocampal circuitry may be a necessary, but perhaps not sufficient, prerequisite for the observed functional recovery in aged rats with severe impairments in spatial learning abilities.
Abstract: Grafts of fetal septal tissue rich in cholinergic neurons were implanted as a dissociated cell suspension into the depth of the hippocampal formation in aged rats with severe impairments in spatial learning abilities. After 2 1/2 to 3 months, the rats with grafts, but not the controls, had improved their performance in a spatial learning test. Their improvement was due, at least in part, to an increased ability to use spatial cues in the task. In all animals the grafts had produced an extensive acetylcholinesterase-positive terminal network in the surrounding host hippocampal formation. Thus, the action of cholinergic neurons in the graft onto elements in the host hippocampal circuitry may be a necessary, but perhaps not sufficient, prerequisite for the observed functional recovery.
365 citations
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344 citations
TL;DR: It is reported here that grafted fetal striatal neurones implanted into the IA-lesioned striatum can significantly ameliorate the lesion-induced locomotor hyperactivity and at least partly normalize the metabolic hyperactivity in the extrapyramidal neuronal system.
Abstract: In rats, striatal neuronal destruction by so-called excitotoxic amino acids, kainic acid or ibotenic acid (IA) produce neuropathological and neurochemical changes in the basal ganglia which resemble those seen in patients with Huntington's chorea. Such lesioned animals show a behavioural syndrome which is reminiscent of the cardinal symptoms of the disease, accompanied by a substantial increase in local cerebral metabolic activity in several striatal target structures within the extrapyramidal motor system. The study was designed to explore the potential of grafted fetal striatal neurones implanted into the IA-lesioned striatum to compensate for the structural, neurochemical, metabolic and behavioural defects of IA-lesioned rats. Extending previous studies, we report here that such striatal implants can significantly ameliorate the lesion-induced locomotor hyperactivity and at least partly normalize the metabolic hyperactivity in the extrapyramidal neuronal system.
302 citations
TL;DR: An analysis of interactions between spatial distribution and size of seabird breeding colonies is presented and support is provided for Ashmole's suggestion that seabirds numbers may be limited by intraspecific competition for food around colonies during the breeding season.
Abstract: There is long-standing disagreement over the way in which seabird populations are regulated1. They may be regulated by density-dependent mortality during winter as a consequence of food shortage2–4, shortage of nest sites5–7, social factors8, or not regulated at all9. Ashmole10,11 argued that for tropical seabirds, density-dependent mortality of adults outside the breeding season is most unlikely because intraspecific competition for food close to the colony would result in prey depletion, causing adults to travel increasing distances for food as colony size increased.Breeding numbers could be regulated through a density-dependent reduction in reproductive output resulting from reduced rates of provisioning of chicks. This mechanism may not apply to seabird colonies in higher latitudes, however, because seasonal production might provide superabundant food supplies during the breeding season. Recent studies of the quantity of food consumed by breeding seabirds12–15 suggest that prey depletion also occurs in temperate regions and invites a critical test of Ashmole's hypothesis. We present here an analysis of interactions between spatial distribution and size of seabird breeding colonies and provide support for Ashmole's suggestion that seabird numbers may be limited by intraspecific competition for food around colonies during the breeding season.
296 citations
TL;DR: The immunosuppressive effect of ultraviolet radiation in the sunburn spectrum in man and animals may be related to the increased incidence of cutaneous malignancy, actinic keratoses, and warts.
281 citations
TL;DR: In this article, a condensation reaction between the terminal hydroxyl groups present in the original polymer and the terminal carboxyl groups were either originally present or formed in the chain scission process.
239 citations
TL;DR: Turnstones, Arenaria interpres, and purple sandpipers, Calidris maritima, show very similar increases in the level of vigilance with decreasing visibility, but achieve these increases by different means: turnstones lengthen the duration of each vigilant scan, while purple Sandpipers scan more often.
TL;DR: In this paper, it was shown that poly(d)-β-hydroxybutyric acid thermally degrades quantitatively under vacuum to volatile products at temperatures up to 338°C.
TL;DR: The allocation of time to anti-predatory behavior in migratory ruddy turnstones (adults) was found to decrease prior to migration, with the cost of a reduced rate of resource accumulation outweighing the additional risk of predation which results from the decrease in vigilance.
Abstract: Many birds accumulate fat reserves prior to departure on long distance migration. Since there will be an increased food requirement during the pre-migratory period, it is to be expected that more time will be invested in foraging, at the expense of other activities. The allocation of time to anti-predatory behavior in migratory ruddy turnstones (adults) was found to decrease prior to migration (Fig. 1); non-migratory individuals (juveniles) showed no decrease over the same time period (Fig. 2). This is interpreted as a change in the optimal adult behavior, the cost of a reduced rate of resource accumulation outweighing the additional risk of predation which results from the decrease in vigilance.
TL;DR: For example, observations of the dark side of the planet Venus at infrared wavelengths between 1.5 and 2.5 µm have shown it to be anomalously bright in portions of this waveband, and to exhibit structured cloud patterns whose rotation period is longer than that of any other clouds as discussed by the authors.
Abstract: Observations of the dark side of the planet Venus at infrared wavelengths between 1.5 and 2.5 µm have shown it to be anomalously bright in portions of this waveband, and to exhibit structured cloud patterns whose rotation period is longer than that of any other clouds.
TL;DR: A number of specific methodological issues have arisen in studies of the social, emotional, and behavioural sequelae of head injury; the use of control groups may help disentangle specific and non-specific effects.
Abstract: A number of specific methodological issues have arisen in studies of the social, emotional, and behavioural sequelae of head injury. The accounts given by patients and relatives may differ: Patients may lack insight, and relatives – who are often under considerable stress – may themselves give distorted accounts. Moreover, the sequelae of head injury may not all be specific to brain injury but may include effects common to other forms of traumatic injury: The use of control groups may help disentangle specific and non-specific effects.
TL;DR: In this article, the products and general characteristics of the thermal degradation of poly(d)-β-hydroxybutyric acid have been accounted for in terms of a comprehensive reaction mechanism.
TL;DR: Evidence of myc gene transduction by feline leukaemia virus in several spontaneous lymphoid tumours of cats suggests that recombinant viruses carrying oncogenes may be much more involved in oncogenesis in natural conditions than previously recognized.
Abstract: Evidence of myc gene transduction by feline leukaemia virus in several spontaneous lymphoid tumours of cats suggests that recombinant viruses carrying oncogenes may be much more involved in oncogenesis in natural conditions than previously recognized.
TL;DR: A striking finding was that flow density changed abruptly (a tenfold variation in flow within a 1 to 2 mm interval) at the edge of the pathological lesion, suggesting that penumbral conditions may exist in only a very narrow zone 4 hours after onset of focal ischemia.
Abstract: We studied local cerebral blood flow, as measured by autoradiography with digital image processing and by tissue morphology, in six rats 4 hours after occlusion of the proximal middle cerebral artery. A consistent, three-dimensional pattern of graded reductions in local cerebral blood flow involved the affected hemisphere, with a densely ischemic zone (local cerebral blood flow less than 3 ml/100 gm/min) in the dorsolateral caudate putamen and the adjacent frontoparietal cortex. In the frontoparietal cortex, the normal laminar pattern of local cerebral blood flow was disrupted, and there was a transcortical gradient in flow, with pronounced ischemia in deeper layers and relatively preserved superficial flow. Comparisons of autoradiographic findings with histopathological abnormalities in adjacent frozen sections showed that the region of ischemic damage corresponded closely with the area of greatest reduction in blood flow. Although around this region local cerebral blood flow increased centrifugally, a striking finding was that flow density changed abruptly (a tenfold variation in flow within a 1 to 2 mm interval) at the edge of the pathological lesion. Penumbral conditions may therefore exist in only a very narrow zone 4 hours after onset of focal ischemia. After occlusion of a major cerebral artery, the pattern of local cerebral blood flow changes appears to depend on interactions among vascular architecture, reductions in perfusion pressure, alterations in metabolic demands, and variations in local vascular resistance.
TL;DR: In this article, the authors discuss some of the ethical issues raised by studies of predator-prey and aggressive interactions when these involve artificially-staged encounters, and propose that the use of model predators should be considered, the number of subjects kept to a minimum and the experiments made as short as possible.
TL;DR: The pharmacological and immunocytochemical results strongly indicate the existence of a novel perivascular neuronal system containing NPY, which mediates contraction of cerebral blood vessels and NPY is colocalized with NA in sympathetic nerves.
Abstract: Plexuses of nerve fibres containing neuropeptide Y (NPY)-like immunoreactivity invest pial arteries belonging to the circle of Willis, pial arterioles, occasionally penetrating arterioles and large veins. A more sparse supply of NPY-like fibres were observed around pial veins and venules. The NPY-immunoreactive fibres are located within the adventitia or at the adventitia-media border. Only occasional fibres are present in cerebral vessels of animals in which the superior cervical ganglion has been removed one week previously. Administration of NPY resulted in strong, concentration-dependent contractions of isolated feline middle cerebral arteries whereas administration of avian pancreatic polypeptide (APP) elicited weak contractions. In chloraloseanaesthetized cats, perivascular microapplication of NPY in situ resulted in marked concentration-dependent contractions of cerebral pial arterioles (34.7 +/- 6.6%; maximum decrease in calibre with NPY. Perivascular administration of NPY resulted in the constriction of pial veins but the magnitude of the venous calibre reductions was smaller than the response of arterioles at each reductions was smaller than the response of arterioles at each concentration examined. APP did not elicit contraction of pial arterioles or veins during in situ conditions. The pharmacological and immunocytochemical results strongly indicate the existence of a novel perivascular neuronal system containing NPY, which mediates contraction of cerebral blood vessels and NPY is colocalized with NA in sympathetic nerves.
TL;DR: The centipedes and possible insects found at a new fossil site near Gilboa, New York, may represent the earliest records known for these groups of terrestrial arthropods.
Abstract: A new fossil site near Gilboa, New York, is one of only three where fossils of terrestrial arthropods of Devonian age have been found. The new Gilboan fauna is younger than the other two but richer in taxa. Fragmentary remains and nearly whole specimens assigned to Eurypterida, Arachnida (Trigonotarbida, Araneae, Amblypygi, and Acari), Chilopoda [Craterostigmatomorpha(?) and Scuterigeromorpha(?)], and tentatively to Insecta (Archaeognatha) have been found. The centipedes and possible insects may represent the earliest records known for these groups.
TL;DR: Operating in ultraclean air and the prophylactic use of antibiotics have been found to reduce the incidence of joint sepsis confirmed at re-operation, after total hip or knee-joint replacement.
Abstract: Operating in ultraclean air and the prophylactic use of antibiotics have been found to reduce the incidence of joint sepsis confirmed at re-operation, after total hip or knee-joint replacement. The reduction was about 2-fold when operations were done in ultraclean air, 4.5-fold when body-exhaust suits also were worn, and about 3- to 4-fold when antibiotics had been given prophylactically. The effects of ultraclean air and antibiotics were additive. Wound sepsis recognized during post-operative hospital stay was, however, reduced by these measures only when it had been classed as major wound sepsis. This was reported after 2.3% of operations done without antibiotic cover in conventionally ventilated operating rooms. Joint sepsis was much more frequent after wound infection and especially after major wound sepsis, although most cases of joint sepsis were not preceded by recognized wound sepsis. This was particularly noticeable after major wound sepsis associated with Staphylococcus aureus; after 37 such infections the same species was subsequently found in the septic joint of 11 patients. The sources of wound colonization with Staph. aureus, when this was not followed by joint sepsis, appeared to differ widely from those where joint sepsis occurred later. Operating-room sources could be found for most of the latter and the risk of infection appeared to be similar with respect to any carrier in the operating room whether a member of the operating team or the patient. For wound colonization that was not followed by joint sepsis, operating-room sources could only be inferred for fewer than half and of these more than one half appeared to be related to strains carried by the patient at the time of operation. During the follow-up period, which averaged about 2 1/4 years with a maximum of four years, there were, in addition to the 86 instances of deep joint sepsis confirmed at re-operation, 85 instances in which sepsis in the joint was suspected during this period but was not confirmed, because re-operation on the joint was not done. The incidence of suspected joint sepsis was, like that of confirmed joint sepsis, less after operations done in ultraclean air: 1/2.5, or with prophylactic antibiotics, 1/2.3 Although re-operation was more frequent on the knee-joint than on the hip, and pain after the initial operation was more frequent after knee operations, there was no evidence that this was the result of any increased risk of infection.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: It was concluded that the primary site of action of crotoxin was hydrolysis of the sarcolemmal membrane and that mitochondrial changes were associated with calcium accumulation in response to an altered internal environment.
TL;DR: It is shown that the properties of this enzyme from Bryophyllum fedtschenkoi undergo marked changes between night and day; the night form is much less sensitive to feedback inhibition by malate than is the day form.
TL;DR: Echinochrome-A dissolved in sea water, with the aid of mammalian proteins as dispersants, was bactericidal or bacteriostatic towards six out of seven strains of marine gram-negative and gram-positive bacteria.
Abstract: 1. 1. The concentrations of echinochrome-A in coelomic fluid from healthy specimens of the sea urchin Echinus esculentus (L.) ranged from 3 to 60 μg/ml, with a geometric mean of 14 μg/ml. 2. 2. Echinochrome-A (50 μg/ml) dissolved in sea water, with the aid of mammalian proteins as dispersants, was bactericidal or bacteriostatic towards six out of seven strains of marine gram-negative and gram-positive bacteria. 3. 3. Echinochrome-A is suggested as a major factor in the bactericidal activity of coelomic fluid from E. esculentus.
TL;DR: The effect of mixed species flocking on vigilance is investigated in two species of wading bird wintering on rocky shores, finding that both turnstones and purple sandpipers ‘share’ vigilance with conspecifics, but also with some other waders; the extent of sharing appears to depend on the relative size of, and habitat overlap with, the other species.
TL;DR: In this article, a wide range of stress states have been generated using axisymmetric and plane strain notched tensile specimens which have been analysed by elastic-plastic finite element analysis.
Abstract: A wide range of stress states has been generated using axisymmetric and plane strain notched tensile specimens which have been analysed by elastic-plastic finite element analysis. Observations of voids on metallographic sections have been combined with calculated deformation histories and the hole growth equations to determine the local conditions for hole nucleation and the strength of the particle-matrix interface. These calculations show that nucleation is a statistical event for which the radial stress at the particle/matrix interface has been determined. Subsequent calculations give the local conditions at void coalescence in the average material and in statistical inhomogeneities. The statistics of the inclusion distribution determine the size scale over which void coalescence must occur in order to create a crack-like defect.
TL;DR: Evidence presented in this paper suggests that the gene in which the ts1204 and ts1208 lesions map encode a structural polypeptide encodes a structural Polymethine-like structure.
TL;DR: It is concluded that inhibitory nerve stimulation in the bovine retractor penis muscle produces a relaxation that is mediated by cyclic GMP, although some substances relax the muscle without affecting cyclicGMP levels.
Abstract: Field stimulation of the non-adrenergic, non-cholinergic inhibitory nerves to the bovine isolated retractor penis muscle evoked a relaxation that was preceded by a rise in the tissue content of cyclic GMP. There was no change in the content of cyclic AMP. The selective cyclic GMP phosphodiesterase inhibitor, 2-o- propoxyphenyl -8- azapurin -6-one (M&B 22948), elevated the tissue's cyclic GMP content, and potentiated both the relaxation and the rise in cyclic GMP produced by inhibitory nerve stimulation. Sodium nitroprusside and an inhibitory factor extracted from the bovine retractor penis muscle mimicked the effects of inhibitory nerve stimulation in that they each produced relaxation associated with a selective rise in cyclic GMP concentration. Haemoglobin (in the form of erythrocyte haemolysate) and N- methylhydroxylamine , which are known to block guanylate cyclase, blocked the relaxation and the rise in cyclic GMP content produced by inhibitory nerve stimulation, inhibitory factor and sodium nitroprusside. Haemoglobin itself caused a rise in muscle tone and at the same time reduced the cyclic GMP content of the tissue. 8-Bromocyclic GMP, a permeant derivative of cyclic GMP, produced a relaxation of the muscle that, as expected, was not blocked by haemoglobin. Vasoactive intestinal polypeptide, prostaglandin E1 and forskolin each produced relaxation associated with a selective rise in cyclic AMP content. Their effects were not blocked by haemoglobin or N- methylhydroxylamine . It is concluded that inhibitory nerve stimulation in the bovine retractor penis muscle produces a relaxation that is mediated by cyclic GMP, although some substances relax the muscle without affecting cyclic GMP levels. The results are also compatible with the view that the extracts of muscle contain the inhibitory neurotransmitter.