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Results for “Functional perturbation”

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PubMed2002

Effects of prenatal protein malnutrition on the hippocampal formation.

In this review we have assessed the effects of prenatal protein malnutrition on the hippocampal formation of the developing brain. In investigating this insult in the hippocampal neuronal model we have concentrated on aspects of enhanced inhibition we have shown in our earlier studies. Since this involves particular attention to the GABAergic interneurons we have examined the complex interneuronal networks of the hippocampal formation and their neurotransmitter afferent inputs, particularly the serotonergic system from the midbrain raphé nuclei. A variety of combinations of specialized interneurons are discussed in terms of how malnutrition insults perturb function in these inhibitory and disinhibitory networks. Pathological enhancement of inhibition manifests itself by diminished plasticity, alterations in theta activity and deficits in long-term learning behaviors. Long-term inhibition in select GABA interneuron systems may form a major derangement seen following prenatal protein malnutrition. The focus of this study is to relate enhanced inhibition to the several forms of inhibitory systems present in the hippocampal formation and develop hypotheses as to the primary derangements that may account for pathological inhibition in prenatal malnutrition.

Animals↗

PubMed2002

Vocal parameters of aerobic instructors with and without voice problems.

Aerobic instructors frequently experience vocal fatigue and are at risk for the development of vocal fold pathology. Six female aerobic instructors, three with self-reported voice problems and three without, served as subjects. Measures of vocal function (perturbation and EGG) were obtained before and after a 30-minute exercise session. Results showed that the group with self-reported voice problems had greater amounts of jitter, lower harmonic-to-noise ratios, and less periodicity in sustained vowels overall, but no significant differences in measures of perturbation and EGG were found before and immediately after instruction. Measures of vocal parameters showed that subjects with self-reported voice problems projected with relatively greater vocal intensity and phonated for a greater percentage of time across beginning, middle, and ending periods of aerobic instruction than subjects with no reported voice problems.

Adult↗

PubMed1978

Properties of radiolabeled alpha-bungarotoxin derivatives and their interaction with nicotinic acetylcholine receptors.

Column-purified monoiodinated, diiodinated, and tritiated derivatives of alpha-bungarotoxin (alpha-Bgt) are distinguished on the basis of their ultraviolet absorption and circular dichroism (CD) spectra. The pattern of changes in CD spectra on incorporation of iodine into a single tyrosine residue of alpha-Bgt and the widespread wavelength distribution of these effects are interpreted as reflecting primary chemical modification of the tyrosine chromophore as well as vicinal and global secondary structural changes. Native and tritiated alpha-Bgt are shown to be more effective than iodinated alpha-Bgt derivatives in competing for specific toxin binding sites on putative nicotinic acetylcholine receptors (nAChR) derived from rat brain reflecting functional perturbation of the modified toxin. In contrast, both membrane-bound and solubilized nAChR from Torpedo californica electroplax display little or no specific binding preference for native toxin, nor are there significant differences in lethal potency of alpha-Bgt derivatives toward mice. These results suggest that peripheral and putative central nAChR may differ in their alpha-Bgt binding properties and suggest the usefulness of modified toxin in detecting those subtle differences.

Animals↗

PubMed2002

Comparative proteomics as a new tool for exploring human mitochondrial tRNA disorders.

More than 70 different point mutations in human mitochondrial tRNA genes are correlated with severe disorders, including fatal cardiopathies, encephalopathies, myopathies, and others. So far, investigation of the molecular impact(s) of mutations has focused on the affected tRNA itself by seeking structural and/or functional perturbations capable of interfering with synthesis of the 13 mitochondrion-encoded subunits of respiratory chain complexes. Here, a proteomic approach was used to investigate whether such mutations would affect the pattern of mitochondrial proteins at a broader level. Analysis of several hundred mitochondrial proteins from sibling cybrid cell lines by two-dimensional electrophoresis, an approach that takes into account all regulatory steps of mitochondrial and nuclear gene expression, indeed reveals a number of up- and downregulated proteins when healthy and single-point-mutation-carrying mitochondria representative of either MELAS or MERRF syndrome were compared. Assignment by mass spectrometry of the two proteins which exhibit obvious large quantitative decreases in the levels of both pathologic mitochondria identified nuclear-encoded subunits of cytochrome c oxidase, a respiratory chain complex. This clearly shows a linkage between the effects of mutations in mitochondrial tRNA genes and the steady-state level of nuclear-encoded proteins in mitochondria. It opens new routes toward a large-scale exploration of potential proteic partners involved in the genotype-phenotype correlation of mitochondrial disorders.

Amino Acid Sequence↗

PubMed2002

Structural defects within the carbamate tunnel of carbamoyl phosphate synthetase.

The X-ray crystal structure of carbamoyl phosphate synthetase (CPS) from Escherichia coli has unveiled the existence of two molecular tunnels within the heterodimeric enzyme. These two interdomain tunnels connect the three distinct active sites within this remarkably complex protein and apparently function as conduits for the transport of unstable reaction intermediates between successive active sites. The operational significance of the ammonia tunnel for the migration of NH3 is supported experimentally by isotope competition and protein modification. The passage of carbamate through the carbamate tunnel has now been assessed by the insertion of site-directed structural blockages within this tunnel. Gln-22, Ala-23, and Gly-575 from the large subunit of CPS were substituted by mutagenesis with bulkier amino acids in an attempt to obstruct and/or hinder the passage of the unstable intermediate through the carbamate tunnel. The structurally modified proteins G575L, A23L/G575S, and A23L/G575L exhibited a substantially reduced rate of carbamoyl phosphate synthesis, but the rate of ATP turnover and glutamine hydrolysis was not significantly altered. These data are consistent with a model for the catalytic mechanism of CPS that requires the diffusion of carbamate through the interior of the enzyme from the site of synthesis within the N-terminal domain of the large subunit to the site of phosphorylation within the C-terminal domain. The partial reactions of CPS have not been significantly impaired by these mutations, and thus, the catalytic machinery at the individual active sites has not been functionally perturbed.

Alanine↗

PubMed1997

Mechanism of the synergistic end-product regulation of Bacillus subtilis glutamine phosphoribosylpyrophosphate amidotransferase by nucleotides.

De novo purine nucleotide synthesis is regulated, at least in part, by end-product inhibition of glutamine PRPP amidotransferase. An important feature of this inhibition is the fact that certain synergistic nucleotide pairs give more than additive inhibition. The physiological importance of synergism is in amplifying regulation by the adenine and guanine nucleotide end products of de novo synthesis. Using a new method to quantitate synergism, ADP plus GMP were confirmed [Meyer, E., and Switzer, R. L. (1978) J. Biol. Chem. 254, 5397-5402] to give strong synergistic inhibition of Bacillus subtilis glutamine PRPP amidotransferase. An X-ray structure of the ternary enzyme.ADP.GMP complex established that ADP binds to the allosteric A site and GMP to the catalytic C site. GMP increased the binding affinity of ADP for the A site by approximately 20-fold. Synergism results from a specific nucleotide-nucleotide interaction that is dependent upon a nucleoside diphosphate in the A site and a nucleoside monophosphate in the C site. Furthermore, synergism is enhanced by the competition between nucleotide inhibitor and PRPP substrate for the C site. Purine base specificity results from a backbone carbonyl interaction of Lys305' with the 6-NH2 group of adenine in the A site and a Ser347 Ogamma interaction with the 2-NH2 group of guanine in the C site. Steric considerations favor binding of the nucleoside diphosphate to the A site. Site-directed replacements of key residues increased the nucleotide concentrations needed for 50% inhibition and in some cases perturbed synergism. Mutations in either of the nucleotide sites perturbed function at both sites, supporting the important role of synergism.

Adenosine Diphosphate↗

PubMed1998

Structure changes in hemoglobin upon deletion of C-terminal residues, monitored by resonance Raman spectroscopy.

Loss of C-terminal residues in hemoglobin raises oxygen affinity and reduces both cooperativity and the Bohr effect. These functional changes are expected from the loss of C-terminal salt bridges, which are seen crystallographically to stabilize the T quaternary structure. Ultraviolet resonance Raman (UVRR) difference spectroscopy confirms that the strength of the T state contacts is diminished when the C-terminal and also the penultimate residues are removed chemically. Deoxy minus CO difference signals arising from the Trpbeta37-Aspalpha94 and Tyralpha42-Aspbeta99 H bonds at the alpha1 beta2 subunit interface are diminished, and at pH 9, the difference spectra reveal a shift to the R quaternary structure. These effects are small for desHisbeta146 Hb and large for desArgalpha141 Hb, consistent with the order of functional changes. In addition, the H bond between the A and E helices is strengthened by removal of Argalpha141 and is further strengthened when the effector molecule IHP (inositol hexaphosphate) is added to deoxy-desArgalpha141 Hb or when its pH is lowered to 5.8. This effect is attributed to the loss of the C-terminal anchor of the alpha chain H helix, which supports the F and A helices. The beta chain is not as sensitive because it has extra F-H interhelix H bonds. Removal of both Hisbeta146 and Tauyrbeta145 produce UVRR changes which are intermediate between desHisbeta146 and desArgalpha141 Hb, although the functional consequences are greater than for desArgalpha141 Hb. Removal of Tyralpha140 as well as Argalpha141 abolishes cooperative binding as well as the Bohr effect, and the UVRR difference signals are also lost, suggesting that quaternary constraints are removed in both the T and the R states. When the approximately 220 cm-1 iron-histidine stretching vibration of the deoxy-proteins is examined, using Raman excitation in resonance with the heme Soret band, the frequency is observed to diminish toward that of deoxyHb A (215 cm-1) as the pH is lowered and IHP is added and to increase toward a completely relaxed value (223 cm-1) as the pH is raised to 9. The relaxation is in the same order as the functional perturbations: desHisbeta146 < desArgalpha141 < desHisbeta146-Tyrbeta145 < desArgalpha141-Tyralpha140. However, even desArgalpha141-Tyralpha140 Hb shows significant reduction in the Fe-His frequency as IHP is added at low pH. The Fe-His frequency is sensitive to both tertiary and quaternary structure changes and is a global indicator of forces at the heme. The order of affinity changes can be understood on the basis of the number of stabilizing H bonds between the F and H helices. Titration curves of the Fe-His frequency against pH are not sigmoidal, consistent with a multiplicity of contributions to the Bohr effect.

Adult↗

PubMed1999

Transducer-binding and transducer-mutations modulate photoactive-site-deprotonation in sensory rhodopsin I.

Sensory rhodopsin I (SRI) is a seven-transmembrane helix retinylidene protein that mediates color-sensitive phototaxis responses through its bound transducer HtrI in the archaeon Halobacterium salinarum. Deprotonation of the Schiff base attachment site of the chromophore accompanies formation of the SRI signaling state, S(373). We measured the rate of laser flash-induced S(373) formation in the presence and absence of HtrI, and the effects of mutations in SRI or HtrI on the kinetics of this process. In the absence of HtrI, deprotonation occurs rapidly (halftime 10 micros) if the proton acceptor Asp76 is ionized (pK(a) = approximately 7), and only very slowly (halftime > 10 ms) when Asp76 is protonated. Transducer-binding, although it increases the pK(a) of Asp76 so that it is protonated throughout the range of pH studied, results in a first order, pH-independent rate of S(373) formation of approximately 300 micros. Therefore, the complexation of HtrI facilitates the proton-transfer reaction, increasing the rate approximately 50-fold at pH6. Arrhenius analysis shows that HtrI-binding accelerates the reaction primarily by an entropic effect, suggesting HtrI constrains the SRI molecule in the complex. Function-perturbing mutations in SRI and HtrI also alter the rate of S(373) formation and the lambda(max) of the parent state as assessed by laser flash-induced kinetic difference spectroscopy, and shifts to longer wavelength are correlated with slower deprotonation. The data indicate that HtrI affects electrostatic interactions of the protonated Schiff base and not only receives the signal from SRI but also optimizes the photochemical reaction process for SRI signaling.

Archaeal Proteins↗

PubMed2005

Dimensional effects on the LO-TO splitting in CF4: first-principles and infrared absorption studies.

The development of longitudinal optical-transverse optical (LO-TO) modes in CF(4) has been studied experimentally and theoretically as a function of dimensionality. Infrared absorption experiments for CF(4) adsorbed on single-walled carbon nanotubes indicate a lack of LO-TO splitting at low coverage and a gradual appearance of LO-TO modes as the coverage of CF(4) on the nanotubes is increased. We have performed density functional perturbation theory calculations for the vibrational frequencies, IR absorption spectra, and phonon density of states for CF(4) in one, two, and three dimensions. The calculations demonstrate that LO-TO splitting in 1D is qualitatively different from that computed for 2D or the bulk. The magnitude of the splitting in 1D is about one-half that computed for the bulk, and the LO mode is very weakly blue-shifted in 1D. We predict that the phonon density of states changes dramatically as the dimensionality of the crystal is changed. This prediction can be tested experimentally via inelastic neutron scattering. We conclude that LO-TO splitting can be used as a probe to identify 1D states of matter.

Journal Article↗

PubMed2004

L-shaped three-center two-electron (C-C-C)+ bonding array.

The structures and reactivities of the complexes between carbenium ions (R(+)) and acetylene or propyne have been investigated with the aid of electron-correlated quantum mechanical calculations (hybrid density functional, perturbation theory, and coupled cluster methods). Depending on the R group, the acetylene/carbenium ion interaction can produce either an "open" 3c-2e structure or the conventional vinyl cation structure. The "open" 3c-2e C-C-C bonding geometry exists as a minimum for R = methyl and primary/secondary/tertiary alkyl, and hence is the most notable. The alignment of three carbon centers is neither bridged nor linear, but L-shaped, and represents a new type of "open" 3c-2e bonding that has so far escaped proper attention.

Journal Article↗

PubMed2006

Rotationally resolved optical rotation and circular dichroism effects for symmetric top molecules induced by a resonant circularly polarized pumping optical field.

The rotationally resolved laser-induced optical activity including the laser-induced optical rotation (LIOR) and laser-induced circular dichroism (LICD) effects of an IR probing light pumped by a collinear intense resonant circularly polarized light dependent on the third-order susceptibility due to the pure electric dipole interaction for achiral symmetric top molecules in the gas phase is discussed theoretically. The laser-induced optical activity contains four distinct contributions named A, B, C, and D terms: the B term of the LIOR and LICD arising from the rotational wave function perturbed by the pumping light is deduced using the semiclassical perturbation theory, and the expressions for A, C, and D terms, respectively, due to the ac Stark effect, the Boltzmann statistical redistribution, and the alteration of occupation polability, are obtained from previous results [Zheng, R.-H.; Chen, D.-M.; Wei, W.-M.; He, T.-J.; Liu, F.-C. J. Chem. Phys. 2004, 121, 6835]. The microwave-IR double resonant spectrum is proposed to detect the LIOR and LICD effects. As an example, the LIOR and LICD for the HCF(3) molecules in the conditions of 298.15 K and 0.3 Torr when the IR probing light sweeps over the rotational-vibrational transition of the v(5) and v(1) modes and the right circularly polarized microwave pumping light with the intensity of 1 kW cm(-2) at the resonant frequency 40.84 GHz are calculated on the basis of the B3LYP/6-311++G* computations. The theoretical results indicate that the B term can be of the same order of magnitude as the A and D terms, and the LIOR and LICD can be measurable in comparison to the rotationally resolved MVCD. The laser-induced optical activity may provide useful new information and form a basis for a different kind of optical activity spectroscopy.

Circular Dichroism↗

PubMed2002

Direct NMR observation and DFT calculations of a hydrogen bond at the active site of a 44 kDa enzyme.

A hydrogen bond between the amide backbone of Arg7 and the remote imidazole side chain of HisIO6 has been directly observed by improved TROSY-NMR techniques in the 44 kDa trimeric enzyme chorismate mutase from Bacillus subtilis. The presence of this hydrogen bond in the free enzyme and its complexes with a transition state analog and the reaction product was demonstrated by measurement of 15N-15N and 1H-15N trans-hydrogen bond scalar couplings, (2h)J(NN) and (lh)J(HN), and by transfer of nuclear polarization across the hydrogen bond. The conformational dependences of these coupling constants were analyzed using sum-over-states density functional perturbation theory (SOS-DFPT). The observed hydrogen bond might stabilize the scaffold at the active site of BsCM. Because the Arg7-His 106 hydrogen bond has not been observed in any of the high resolution crystal structures of BsCM, the measured coupling constants provide unique information about the enzyme and its complexes that should prove useful for structural refinement of atomic models.

Arginine↗

PubMed1995

Beta 1 integrins mediate adherent phenotype of human erythroblastic cell lines after phorbol 12-myristate 13-acetate induction.

We investigated the effects of phorbol ester (phorbol 12-myristate 13-acetate; PMA) treatment on the adhesive behaviour of three erythroleukaemia cell lines: HEL, LAMA-84 and AP217. In the three cell lines PMA induced an increase in expression of a megakaryocytic marker: alpha IIb beta 3 integrin, but did not promote activation of this receptor. Indeed, an antibody specific for the activated form of alpha IIb beta 3 failed to react with the three cell lines. PMA induction led to different adhesive phenotypes depending on the cell line; in fact LAMA-84 and HEL cells became adherent while AP217 cells remained non-adherent. By studying cell surface receptors we found that the major difference between the adherent and the non-adherent cells was the expression of beta 1 integrins. After PMA induction, beta 1 integrin expression was totally abolished in AP217 cells and the amount of beta 1 mRNA was reduced preventing new synthesis of the subunit. In HEL and LAMA-84 cells, PMA treatment did not alter the overall level of beta 1 integrin but induced a new pattern of alpha-subunit expression: up-regulation of alpha 2 and alpha v subunits and down-regulation of alpha 4 and alpha 5 subunits. Function-perturbing antibodies against beta 1, alpha 4, alpha 5, alpha v and alpha 2 reduced adhesion of HEL cells to fibronectin or collagen, whereas antibodies against beta 3 or alpha v beta 3 did not. Our results favour the involvement of beta 1 integrins in PMA-induced adhesion of erythroleukaemia cells.

Base Sequence↗

PubMed2001

Treatment of abdominally obese men with a serotonin reuptake inhibitor: a pilot study.

OBJECTIVE: To investigate the effects of a selective serotonin reuptake inhibitor (SSRI) on the neuroendocrine and autonomic nervous system perturbations found in abdominal obesity. DESIGN: Treatment for 6 months with citalopram and for 6 months with placebo using a double-blind, cross-over design, with a 2-month wash-out period between treatment periods. SUBJECTS: Sixteen healthy men, 45-60 years, moderately obese and with an abdominal fat distribution. MEASUREMENTS: Anthropometry, three different depression rating scales, serum lipids, testosterone, IGF-I, oral glucose tolerance test (OGTT), pituitary stimulation with corticotropin releasing hormone (CRH), arithmetic stress test, and excretion of cortisol and metoxycatecholamines in urine, collected during 24 h. RESULTS: Cortisol concentrations in the morning were low before treatment, indicating a perturbed function of the hypothalamic-pituitary-adrenal (HPA) axis. After treatment with citalopram morning cortisol concentrations rose to normal. Cortisol concentrations after stimulation with CRH or stress were elevated by citalopram treatment, but urinary cortisol excretion was unchanged. The glucose concentrations after OGTT (120 min) tended to be reduced, with unchanged insulin concentrations, whilst other metabolic values did not change during treatment. Heart rate after administration of CRH, and during laboratory stress test, decreased by treatment with citalopram. Diurnal urinary excretion of metoxycatecholamines tended to decrease. Neither body mass index nor waist/hip circumference ratio decreased. Depression scores were within normal limits before treatment and did not change. CONCLUSION: The results of this pilot study indicate improvements in the regulation of neuroendocrine-autonomic systems as well as metabolism in abdominal obesity during treatment with an SSRI.

Body Constitution↗

PubMed2003

T-cell receptor excisional circles, telomere length, proliferation and apoptosis in peripheral blood mononuclear cells of human immunodeficiency virus-infected individuals after 18 months of treatment induced viral suppression.

This study evaluated the effect of highly active antiretroviral therapy (HAART)-induced viral suppression on T-cell receptor excisional circles (TRECs), telomere length, proliferative responses and spontaneous as well as phytohaemagglutinin (PHA)-stimulated lymphocyte apoptosis in 27 human immunodeficiency virus (HIV)-infected individuals followed for 18 months during HAART. Our results show that HAART significantly increased the level of TRECs in CD4+ cells (P = 0.003) after 18 months of almost continuously suppressed HIV-RNA levels. Lymphocyte proliferative responses and apoptosis levels in patients were significantly lower and significantly higher, respectively, compared with healthy controls. The proliferative response and apoptosis levels did not change during follow up. Changes in telomere length were observed in CD4+ and in CD8+ T cells. The study demonstrated that HAART induces normal TREC levels in the CD4+ T-cell pool. However, the other perturbed functions in T cells indicate that immune reconstitution is incomplete and may need longer viral suppression.

Adult↗

PubMed2002

Person-centered approach to care, teaching, and research in fibromyalgia syndrome: justification from biopsychosocial perspectives in populations.

OBJECTIVES: To describe complex interactions of multiple factors believed to contribute to fibromyalgia syndrome (FMS) at a person-centered level to enhance approaches to care, teaching, and research. The main factors addressed were central nervous system sensory sensitization, autonomic nervous system (ANS) activation, neurohumoral perturbations, and psychosocial and environmental stressors. A person-centered approach is defined as attention to major biopsychosocial issues of affected individuals. METHODS: Literature on classification, mechanistic pathways, course and outcomes, and management of FMS was reviewed to assess applications of person-centered approaches to care, teaching, and research. Various biopsychosocial influences were considered in relation to the heterogeneous subjective manifestations of this illness, including central hyperalgesia, ANS and other neurohumoral perturbations, functional hyperexcitability, nonrestorative sleep, and psychologic distress. RESULTS: A person-centered approach to FMS can expand on and strengthen traditional biomedical concepts. Adding such a focus can help to untangle current controversies in the course, outcomes, and treatment of FMS. A person-centered approach can also help in the subgrouping of affected patients for greater specificity in care programs and in improved clinical investigations. In the biomedical model, diverse symptoms of FMS are often addressed separately and apart from their interconnectedness and linkages to the patient's individualized biopsychosocial factors. However, the causes of FMS symptomatology are not likely to be caused by uniform biologic abnormalities across populations. Rather, the syndrome likely results from personal reactivities to varied multifactorial biopsychosocial influences. Common denominators among individuals may include varying degrees of ANS activation (or personal susceptibility to ANS activation), nonrestorative sleep, negative affectivity, and other central pain sensitization mechanisms, among the pathways reviewed. CONCLUSIONS: Innovative analytical methodologies will need to be developed to more effectively investigate complex interacting biopsychosocial dynamics at a person-centered level, including qualitative research, and multifactorial and multilevel techniques. Adding person-centered approaches to biopsychosocial concepts of FMS promises to show new physiopathogenetic insights and more effective treatment than current biomedical models alone. Person-centered approaches enhance patient-physician relationships and help prioritize patients' goals in mutually derived treatment plans.

Adolescent↗

PubMed1988

Protein C and the endothelium.

With the continued accumulation of clinical and animal studies, it is becoming abundantly clear that the protein C anticoagulant pathway plays a critical role in the regulation of coagulation. Investigations also indicate that this pathway is intimately involved in the interaction of the coagulation and inflammatory systems. Although no direct information is presently available, the function of this pathway is likely depressed in the regions of atherosclerotic plaque. It is clear that monocytes accumulate in this region and release many growth factors and monokines that are capable of endothelial function perturbation. Perturbation of the protein C anticoagulant pathway is one viable mechanism for the hypercoagulable state in this disease. As indicated here, the endothelial cells of the vessel wall play a critical role in the initiation, and possibly expression, of this pathway. Any injury to these cells that affects the proper expression of thrombomodulin, synthesis of protein S, or Factor Va inactivation complex formation could potentially lead to a hypercoagulable state and thrombotic complications. As has been discussed, several inflammatory mediators are already known that fulfill the criteria of endothelial cell perturbants that may lead to such a state. What other entities might have similar effects, either directly or indirectly through induction of cytokines, is not known at this time. A more complete understanding of this critical pathway and the effects of vascular disease on it should lead to a better understanding of many diverse disease processes and potential therapeutic strategies in the future.

Animals↗

PubMed1994

Two-dimensional model of a kicked oscillator: Motion with intermittency.

The phenomenon of intermittency, which arises near a point of degeneracy of an unperturbed Hamiltonian under the influence of a discontinuous perturbation function, is studied in the example of a two-dimensional (2-D) model of a kicked oscillator. This example describes the dynamics of a particle in a cylindrically symmetric potential well subjected to radial kicks which occur periodically in time. The problem is reduced to a Hamiltonian system with N=3/2 degrees of freedom, whose unperturbed Hamiltonian has a degeneracy point. The intermittency is studied numerically and analytically.

Journal Article↗