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G Lowe

Publications and source records attributed to G Lowe.

At least 37 records · Page 2Linked to original sources
PubMed1994

Crystal structure of the mutant D52S hen egg white lysozyme with an oligosaccharide product.

The crystal structure of a mutant hen egg white lysozyme, in which the key catalytic residue aspartic acid 52 has been changed to a serine residue (D52S HEWL), has been determined and refined to a crystallographic R value of 0.173 for all data F > 0 between 8 and 1.9 A resolution. The D52S HEWL structure is very similar to the native HEWL structure (r.m.s. deviation of main-chain atoms 0.20 A). Small shifts that result from the change in hydrogen bonding pattern on substitution of Asp by Ser were observed in the loop between beta-strands in the region of residues 46 to 49. D52S HEWL exhibits less than 1% activity against the bacterial cell wall substrate. Cocrystallisation experiments with the hexasaccharide substrate beta(1-4) polymer of N-acetyl-D-glucosamine (GlcNAc6) resulted in crystals between 5 days and 14 days after the initial mixing of enzyme and substrate. Analysis by laser absorption mass spectrometry of the oligosaccharides present after incubation with native and D52S HEWL under conditions similar to those used for crystal growth showed that after 14 days with native HEWL complete catalysis to GlcNAc3. GlcNAc2 and GlcNac had occurred but with D52S HEWL only partial catalysis to the major products GlcNAc4 and GlcNAc2 had occurred and at least 50% of the GlcNAc6 remained intact. X-ray analysis of the D52S-oligosaccharide complex crystals showed that they contained the product GlcNAc4. The structure of the D52S HEWL-GlcNAc4 complex has been determined and refined to an R value of 0.160 for data between 8 and 2 A resolution. GlcNAc4 occupies sites A to D in the active site cleft. Careful refinement and examination of 2Fo-Fc electron density maps showed that the sugar in site D has the sofa conformation, a conformation previously observed with the HEWL complex with tetra-N-acetylglucosamine lactone transition state analogue, the HEWL complex with the cell wall trisaccharide and the phage T4 lysozyme complex with a cell wall product. The semi-axial C(5)-C(6) geometry of the sofa is stabilised by hydrogen bonds from the O-6 hydroxyl group to the main-chain N of Val109 and main-chain O of Ala107. The sugar in site D adopts the alpha configuration, seemingly in conflict with the observation that the hydrolysis of beta (1-4) glycosidie linkage by HEWL proceeds with 99.9% retention of beta-configuration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Suppression of odorant responses by odorants in olfactory receptor cells.

Odorants activate an inward current in vertebrate olfactory receptor cells. Here it is shown, in receptor cells from the newt, that odorants can also suppress this current, by a mechanism that is distinct from inhibition and adaptation. Suppression provides a simple explanation for two seemingly unrelated phenomena: the anomalously long latency of olfactory transduction and the existence of an "off response" at the end of a prolonged stimulus. Suppression may influence the perception of odorants by masking odorant responses and by sharpening the odorant specificities of single cells.

Acetophenones↗
PubMed1994

The closure of a long-stay psychiatric hospital: a longitudinal study of patients' behavior.

This paper summarises longitudinal data based on repeat assessments of the behavioural functioning of 90 long-stay psychiatric patients. Data were gathered over a period of 4-5 years that spanned a hospital closure and the resettlement of patients in various alternative settings. Time-series analyses of individual data sets showed that resettlement led to no significant behavioural change in the majority of patients. However, some significant behavioural improvements were evidenced for approximately 20% of the group, while behavioural deterioration occurred in approximately 12%. Supplementary findings showed that following resettlement the quality of care provided significantly improved in many respects. However, access to social, recreational or vocational activities was reduced. In addition, the level of physical health symptomatology was shown to increase for this group of patients.

Aged↗
PubMed1994

Group differences in alcohol-creativity interactions.

A repeated-measures, balanced-order design was used to test for the effects of alcohol on creativity as measured by verbal forms of the Torrance Creativity Test. Social drinkers (8 men and 8 women) performed under 2 conditions, alcohol (dose = 0.83 ml ethanol/kg body weight) and a placebo. Significant group differences in the alcohol-creativity interaction were noted in that the performance of higher-scoring (in the placebo condition) subjects was impaired by alcohol whereas that of lower-scoring subjects was enhanced.

Achievement↗
PubMed1993

Nonlinear amplification by calcium-dependent chloride channels in olfactory receptor cells.

The sense of smell is highly evolved in mammals, allowing discrimination between a vast number of odorants, with detection thresholds as low as 10(-17) M (ref. 1). Although several features of mammalian olfactory transduction have been revealed by biochemical and molecular biological studies, the odorant-induced membrane current has remained elusive. In amphibians this current is mediated by cyclic-nucleotide-gated channels, which depolarize the cell by Na+ and Ca+ influx and consequent Cl- efflux through Ca(2+)-dependent Cl- channels. The Cl- current may be absent in mammals, however, because its proposed role is linked to the aquatic habitat of amphibians. Here we show that the transduction current in rat olfactory receptor cells is initiated by cyclic-nucleotide-gated channels. The Cl- current is also present and endows the transduction current with a steep sigmoidal dependence on cyclic AMP concentration in both rat and in an amphibian, indicating a new function for the Cl- channel: nonlinear amplification of the transduction signal, whereby suprathreshold responses are boosted relative to basal transduction noise.

Amphibians↗
PubMed1993

Comparative potency of broad-band and narrow-band phototherapy sources to induce edema, sunburn cells and urocanic acid photoisomerization in hairless mouse skin.

The Philips TL01 narrow-band (311-313 nm) fluorescent lamp provides effective phototherapy for psoriasis and atopic eczema while emitting less erythemogenic radiation than conventional broad-band (e.g. Philips TL12; 270-350 nm) sources. We studied the potency of TL01 and TL12 radiation to induce edema and sunburn cells (SBC) and to photoisomerize naturally occurring trans-urocanic acid (UCA) to cis-UCA in hairless mouse skin. Cis-UCA has immunosuppressive properties and is a putative mediator of UV-induced suppression of immune responses. For each source, there was UV dose dependence for all three responses. Within the dose ranges used, the potency ratio of TL12:TL01 radiation to induce equivalent edema and SBC was about 6:1. However, the potency ratio to induce cis-UCA was less than 2.3:1. Therefore, at a given level of edema or SBC induction, TL01 was more efficient than TL12 at UCA photoisomerization. The TL01 induction of immunomodulating cis-UCA, while causing minimal skin injury, may relate to the therapeutic efficacy of this source in skin conditions with an immunological component.

Albinism↗
PubMed1993

Contribution of the ciliary cyclic nucleotide-gated conductance to olfactory transduction in the salamander.

1. Flash photolysis of caged cyclic nucleotides was used to examine the contribution of the ciliary cyclic nucleotide-gated conductance to olfactory transduction in the tiger salamander. Brief illumination of solitary olfactory receptor cells loaded with 100 microM caged cyclic AMP caused a large inward current (peak amplitude 355 +/- 200 pA; mean +/- S.D. for eleven cells) under whole-cell voltage clamp at -50 mV. 2. The photolysis response was initiated after a latency of 4-12 ms, whereas an odorant response of identical amplitude had a latency of several hundred milliseconds. The amplitudes of both responses exhibited almost identical voltage dependence between -50 and +25 mV, with both reversing near 0 mV. The time courses of the falling phases of odorant and photolysis responses also exhibited similar voltage dependence, both being prolonged at positive voltages. 3. Photolysis of caged cyclic GMP activated a current similar in amplitude and time course to that produced by photolysis of caged cyclic AMP. 4. When the flash was spatially limited to the cilia, the amplitude and duration of the photolysis response increased linearly with the length of the cilia illuminated (for cilia not longer than 30-40 microns) while the latency remained constant at 4-12 ms. The increase in duration was described semi-quantitatively by a model which incorporated diffusion and saturable hydrolysis of cyclic AMP. When the flash was limited to the soma or proximal dendrite, the response latency was proportional to the square of the distance between the illuminated region and the cilia. 5. Dialysis of cells with 500 microM cyclic AMP from a whole-cell electrode under voltage clamp activated a large transient inward current. Simultaneous suction electrode recording showed that this current originated almost entirely from the ciliary membrane. The density of cyclic nucleotide-gated channels was estimated to be 800-fold higher in the cilia than in the soma. 6. Summation of simultaneous odorant and photolysis responses was non-linear, the flash-induced current being enhanced during a small odorant response and attenuated during a large odorant response. Summation of two photolysis responses was similarly non-linear. The data were consistent with odorant stimuli and cyclic AMP both activating a common cyclic nucleotide-gated conductance with a Hill coefficient, n, of 2.0-4.4. For n = 2.5, the basal cyclic AMP concentration was estimated to be less than 20% of the K 1/2, which predicts a basal current of 5.8 pA, less than 2% of the maximum.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambystoma↗
PubMed1992

Evidence for cross-linking DNA by bis-intercalators with rigid and extended linkers is provided by knotting and catenation.

A new series of DNA bis-intercalators is reported in which acridine moieties are connected by rigid and extended pyridine-based linkers of varied length. Cross-linking of DNA by bis-intercalation is inferred from the unwinding and folding of linear DNA induced by the compounds; after ligation and removal of the bis-intercalator, superhelical circles, catenanes and knots that bear a residual imprint of the bis-intercalator are observed. These novel bis-intercalators are of interest because they can be used to probe the spatial organization of DNA, especially near sites of replication, recombination or topoisomerase action where two duplexes must be in close proximity. Preliminary results on the effects of the various compounds on the cloning efficiency of bacteria and replication by permeabilized human cells are also presented.

Acridine Orange↗
PubMed1992

Bisintercalators of DNA with a rigid linker in an extended configuration.

A new class of DNA bisintercalators is reported in which phenanthridinium or acridinium rings are connected by rigid and extended linkers of varied length. Cross-linking of DNA by bisintercalation is inferred from the unwinding and folding of linear DNA induced by the compound; after ligation and removal of the bisintercalator, superhelical circles, catenanes, and knots that bear an imprint of the bisintercalator are observed. These novel bisintercalators are of interest because they can be used to probe the organization of DNA in three-dimensional space, especially near sites of replication, recombination, or topoisomerase action, where two duplexes must be in close proximity.

Acridines↗
PubMed1992

A study of D52S hen lysozyme-GlcNAc oligosaccharide complexes by NMR spectroscopy and electrospray mass spectrometry.

The production of a mutant hen lysozyme is described in which Asp-52, one of the catalytically important residues, is replaced by Ser. The mutant enzyme has very low catalytic activity but NMR studies show that its structure is closely similar to that of the wild-type protein. NMR experiments also show that well defined complexes are formed with GlcNAc4 and GlcNAc6 bound in the active site of the mutant enzyme. These complexes have been examined using electrospray mass spectrometry (ESMS). The most intense peaks arise from the uncomplexed protein indicating that dissociation takes place in the mass spectrometer under the conditions used here. Peaks from minor species corresponding to complexes between the protein and the oligosaccharides are, however, also observed. The possibility that the latter arise from novel covalent enzyme-saccharide complexes is discussed.

Acetylglucosamine↗
PubMed1992

Positive effects of subliminal stimulation on memory.

To assess the effect of subliminally embedded auditory material on short-term recall, 60 volunteer subjects undertook a face-name-occupation memory test before and after a 15-min. intervention. They were randomly assigned into three groups (a control group and two experimental groups) and allocated to one of the following conditions: (1) no sound, (2) supraliminal presentation of relaxing music, and (3) subliminal presentation of memory-improvement affirmations embedded in relaxing music. After intervention, only the subliminal group significantly improved their performance on recall of names.

Adolescent↗
PubMed1991

Studies of inositol analogues as inhibitors of the phosphoinositide pathway, and incorporation of 2-deoxy-2-fluoro-myo-inositol to give analogues of phosphatidylinositol intermediates.

The incorporation of [3H]Ins into PtdIns by exchange of free and lipid-bound inositol moieties occurs via the action of at least two types of Mg2+/Mn(2+)-dependent enzymes in turkey erythrocytes. One is a nucleotide-independent PtdIns/Ins exchange enzyme and its function is, as yet, unknown, whereas the other is CMP-dependent and appears to be an exchange reaction catalysed by PtdIns synthase. The effects of analogues with modifications of the substituent at the 1-, 2-, 3-, 4- and 5-positions on the incorporation of [3H]Ins into PtdIns under both synthase and exchange reaction conditions were investigated in turkey erythrocytes. Analogues causing substantial inhibition of [3H]Ins incorporation were then used in kinetic experiments to determine the type of inhibition involved. The analogues 1-deoxy-1-fluoro-scyllo-inositol and 5-O-methyl-myo-inositol exhibited the greatest effects on the incorporation of [3H]Ins via both the synthase and exchange reactions, and the kinetic analysis indicated that they were competitive inhibitors of Ins. Ki values of 0.37 mM and 2.87 mM were observed for 1-deoxy-1-fluoro-scyllo-inositol under exchange and synthase reaction conditions respectively; similar Ki values of 0.26 mM and 2.80 mM were observed for 5-O-methyl-myo-inositol in the exchange and synthase reactions respectively. The ability of 1-deoxy-1-fluoro-scyllo-inositol and its diastereoisomer, 2-deoxy-2-fluoro-myo-inositol, to act as substrates for the synthase and exchange reactions in turkey erythrocytes was investigated. The radiolabelled derivative of the former analogue was not incorporated into phospholipids, whereas the radiolabelled derivative of the latter analogue was a poor substrate for the synthase and exchange enzymes. In the presence of ATP, the labelled analogue of PtdIns, derived from 2-deoxy-2-fluoro-myo-[2-3H]inositol, appeared to be converted into phosphorylated PtdIns analogues, presumably by the enzymes of the phosphoinositide pathway.

Animals↗
PubMed1991

Phosphatidylinositol synthase and phosphatidylinositol/inositol exchange reactions in turkey erythrocyte membranes.

Unlike human erythrocytes, those from avian species, such as turkeys and chicks, rapidly incorporate myo-[3H]inositol into membrane phospholipids. The mechanisms regulating [3H]Ins labelling of phosphatidylinositol have been investigated using turkey erythrocyte membranes. In the absence of added nucleotides, [3H]inositol incorporation appears to proceed via phosphatidylinositol/inositol exchange, with a Km for inositol of 0.01 mM. The reaction was dependent upon divalent cations, either Mg2+ or Mn2+, with the latter metal ion being the more effective. [3H]Inositol incorporation was accelerated by CMP, especially when the concentration of Ins was greater than the Km for the exchange reaction. CMP-dependent labelling of PtdIns had a Km for inositol of 0.3 mM and for CMP of 0.015 mM. Divalent cations were also required for this reaction: activity peaked at 0.5 mM-Mn2+ and declined at higher concentrations. At relatively high concentrations, Mg2+ was more effective than Mn2+, with peak activity being achieved above 10 mM. CMP-dependent incorporation of [3H]inositol appears to reflect an exchange reaction catalysed by PtdIns synthase. Definitive evidence for the occurrence of PtdIns synthase in turkey erythrocyte membranes was obtained by demonstrating the formation of [14C]CMP-phosphatidate from [14C]CMP. The radioactivity could be efficiently chased from [14C]CMP-phosphatidate in the presence of unlabelled inositol. The detection of PtdIns synthase activity in morphologically simple turkey erythrocytes should help to clarify the subcellular distribution of this important component of the phosphatidylinositol cycle.

Animals↗
PubMed1991

A three-disulphide derivative of hen lysozyme. Structure, dynamics and stability.

A three-disulphide derivative of hen egg-white lysozyme was made by selective reduction and carboxymethylation of one of the four original disulphide bridges. N-Terminal sequencing and two-dimensional 1H-n.m.r. spectroscopy revealed that the disulphide bridge linking cysteine residues 6 and 127 had been modified and that the three remaining disulphide bonds were native-like in nature. Analysis of COSY and NOESY spectra indicated that the three-disulphide lysozyme (CM6.127-lysozyme retains the same secondary and tertiary structure as its four-disulphide counterpart; its stability to pH and temperature is, however, dramatically decreased. N.m.r. spectroscopy was used to characterize the thermal folding and unfolding transition of CM6.127-lysozyme. Not only is the transition still a highly co-operative event, but the enthalpy change associated with folding and unfolding resembles that of intact lysozyme when their differences in thermal stability are taken into consideration. The significance of these results in terms of the folding process of lysozyme is discussed. By contrast with authentic lysozyme, CM6.127-lysozyme was found to exist in an unfolded state at pH 2 at room temperature. N.m.r. spectroscopy and c.d. were used to characterize this state. Unlike their homologous relative, alpha-lactalbumin, which exists in a partially folded molten globule state under these conditions, only residual non-native-like structure persists in the acid-unfolded state of CM6.127-lysozyme. These results indicate that the difference in folding behaviour of lysozyme and alpha-lactalbumin cannot be accounted for simply by their differences in thermal stability.

Animals↗