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PubMed2005

Automated generation of coupled-cluster diagrams: implementation in the multireference state-specific coupled-cluster approach with the complete-active-space reference.

An algorithm for generation of the spin-orbital diagrammatic representation, the corresponding algebraical formulas, and the computer code of the coupled-cluster (CC) method with an arbitrary level of the electronic excitations has been developed. The method was implemented in the general case as well as for specific application in the state-specific multireference coupled-cluster theory (SSMRCC) based on the concept of a "formal reference state." The algorithm was tested in SSMRCC calculations describing dissociation of a single bond and in calculations describing simultaneous dissociation of two single bonds--the problem requiring up to six-particle excitations in the CC operator.

Journal Article↗
PubMed1975

Paired moving charge model of energy coupling. III. Intrinsic ionophores in energy coupling systems.

The experimental basis for the postulated role of intrinsic ionophores in mitochondrial ion transport and energy coupling is summarized. Intrinsic ionophores appear to be linked to, or contained within, specific ionophoroproteins localized in the inner membrane, and the isolation of these ionophores requires their release from the ionophoroproteins. At least ten different species of ionophores have been isolated from the mitochondrion, five of which have been wholly or in part chemically identified. Intrinsic ionophores have been implicated in the activation of inorganic phosphate in ATP synthesis and hydrolysis, and in the contol of the coupling modes. The presence of ionophores in soluble proteins such as troponin and in ATP-energized kinases has been demonstrated.

Biological Transport, Active↗
PubMed1995

Coupling of human D-1 dopamine receptors to different guanine nucleotide binding proteins. Evidence that D-1 dopamine receptors can couple to both Gs and G(o).

Coupling between D-1 dopamine receptors and G proteins in cell lines expressing human D-1 receptors and different G proteins was examined. Pertussis toxin (PTX) treatment of rat pituitary GH4C1 cells significantly reduced, but did not abolish, agonist high affinity binding sites of the D-1 dopamine receptor; in SK-N-MC neuroblastoma cells, PTX failed to have any effect on D-1 high affinity sites. Cholera toxin (CTX) treatment of GH4C1 cells reduced but did not abolish the high affinity sites of D-1 receptors, while in SK-N-MC cells, treatment with CTX abolished all the high affinity sites. Western blot analyses with specific antisera indicated that Gs alpha, Gi1 alpha, Gi3 alpha, and Gq alpha were expressed in both cell lines, while Gi2 alpha and G(o) alpha were expressed in GH4C1 but not SK-N-MC cells. Antisera NEI-805 (anti-Gs alpha) and 9072 (anti-G(o) alpha) immunoprecipitated 24 +/- 4.3 and 34.4 +/- 6.9%, respectively, of G protein-associated D-1 dopamine receptors. Antisera 3646 (anti-Gi1 alpha), 1521 (anti-Gi2 alpha), 1518 (anti-Gi3 alpha), and 0941 (anti-Gq alpha) failed to coimmunoprecipitate appreciable levels of soluble receptors. These data indicate that D-1 dopamine receptors are coupled to both Gs alpha and G(o) alpha but not to Gq alpha.

Animals↗
PubMed2001

Differential conformational requirements for activation of G proteins and the regulatory proteins arrestin and G protein-coupled receptor kinase in the G protein-coupled receptor for parathyroid hormone (PTH)/PTH-related protein.

After stimulation with agonist, G protein-coupled receptors (GPCRs) activate G proteins and become phosphorylated by G protein-coupled receptor kinases (GRKs), and most of them translocate cytosolic arrestin proteins to the cytoplasmic membrane. Agonist-activated GPCRs are specifically phosphorylated by GRKs and are targeted for endocytosis by arrestin proteins, suggesting a connection between GPCR conformational changes and interaction with GRKs and arrestins. Previously, we showed that by substitution of histidine for residues at the cytoplasmic side of helix 3 (H3) and helix 6 (H6) of the parathyroid hormone (PTH) receptor (PTHR), a zinc metal ion-binding site is engineered that prevents PTH-stimulated G(s) activation (Sheikh, S. P., Vilardaga, J.-P., Baranski, T. J., Lichtarge, O., Iiri, T., Meng, E. C., Nissenson, R. A., and Bourne, H. R. (1999) J. Biol. Chem. 274, 17033-17041). These data suggest that relative movements between H3 and H6 are critical for G(s) activation. Does this molecular event play a similar role in activation of GRK and arrestin and in PTHR-mediated G(q) activation? To answer this question, we utilized the two previously described mutant forms of PTHR, H401 and H402, which contain a naturally present histidine residue at position 301 in H3 and a second substituted histidine residue at positions 401 and 402 in H6, respectively. Both mutant receptors showed inhibition of PTH-stimulated inositol phosphate and cAMP generation in the presence of increasing concentrations of Zn(II). However, the mutants showed no Zn(II)-dependent impairment of phosphorylation by GRK-2. Likewise, the mutants were indistinguishable from wild-type PTHR in the ability to translocate beta-arrestins/green fluorescent protein to the cell membrane and were also not affected by sensitivity to Zn(II). These results suggest that agonist-mediated phosphorylation and internalization of PTHR require conformational switches of the receptor distinct from the cAMP and inositol phosphate signaling state. Furthermore, PTHR sequestration does not appear to require G protein activation.

Animals↗
PubMed2004

AGS3 and signal integration by Galpha(s)- and Galpha(i)-coupled receptors: AGS3 blocks the sensitization of adenylyl cyclase following prolonged stimulation of a Galpha(i)-coupled receptor by influencing processing of Galpha(i).

AGS3-LONG and AGS3-SHORT contain G-protein regulatory motifs that interact with and stabilize the GDP-bound conformation of Galpha(i) > Galpha(o). AGS3 and related proteins may influence signal strength or duration as well as the adaptation of the signaling system associated with sustained stimulation. To address these issues, we determined the effect of AGS3 on the integration of stimulatory (Galpha(s)-mediated vasoactive intestinal peptide receptor) and inhibitory (Galpha(i)-mediated alpha(2)-adrenergic receptor (alpha(2)-AR)) signals to adenylyl cyclase in Chinese hamster ovary cells. AGS3-SHORT and AGS3-LONG did not alter the VIP-induced increase in cAMP or the inhibitory effect of alpha(2)-AR activation. System adaptation was addressed by determining the influence of AGS3 on the sensitization of adenylyl cyclase that occurs following prolonged activation of a Galpha(i)-coupled receptor. Incubation of cells with the alpha(2)-AR agonist UK14304 (1 microm) for 18 h resulted in a approximately 1.8-fold increase in the vasoactive intestinal peptide-induced activation of adenylyl cyclase, and this was associated with a decrease in membrane-associated Galpha(i3). Both effects were blocked by AGS3-SHORT. AGS3-SHORT also decreased the rate of Galpha(i3) decay. A mutant AGS3-SHORT incapable of binding G-protein was inactive. These data suggest that AGS3 and perhaps other G-protein regulatory motif-containing proteins increase the stability of Galpha(i) in the membrane, which influences the adaptation of the cell to prolonged activation of Galpha(i)-coupled receptors.

Adenylyl Cyclases↗
PubMed1991

Precise charge-coupling calculations for finite difference diffusion problems using a modification of the add-on algorithm Q-COUPLE.

This note describes a minor modification to the recently published algorithm 'Q-COUPLE' designed for adding charge-charge interactions between diffusing species to time-dependent one-dimensional finite difference diffusion calculations. The original proposal concerned a simple way of doing this for Crank-Nicolson central time-difference schemes, and gave useful, but only approximate, agreement with theory in tests where the charge-coupling could also be calculated analytically. The new, slightly modified algorithm, when used with explicit (forward time-difference) modelling, gave analytically exact results for the charge interaction part of a similar trial calculation.

Algorithms↗
PubMed1989

Inductively coupled plasma mass spectrometry and atomic emission spectrometry coupled to high-performance liquid chromatography for speciation and detection of organotin compounds.

Inductively coupled plasma mass spectrometry (ICP/MS) is utilized as a detector for several organotin species separated by high-performance liquid chromatography. Detection limits obtained by ICP/MS are 3 orders of magnitude lower than those obtained with inductively coupled plasma atomic emission spectrometry (ICP/AES) detection under the same chromatographic conditions. Chromatographic detection limits are higher than conventional solution nebulization for the same compound by a factor of 20. Ion-exchange chromatography yields linear response over 3 orders of magnitude, while ion pair chromatography gives a linear response of only 2 orders of magnitude as a result of poor resolution. The relative standard deviation for the injection of 20 ng of tin compounds is less than 10%.

Chromatography, High Pressure Liquid↗
PubMed1979

Energetic coupling in the primary processes of photosynthesis in Chromatium. pH dependence of delayed fluorescence, electron transfer and degree of coupling.

The effects of pH on the thermodynamic properties of the proton-translocating cyclic electron transfer system in a purple photosynthetic bacterium Chromatium vinosum were studied. Two thermodynamic parameters, the flux (Je) and force (deltamue) of the electron transfer process, were analyzed. The rate of electron transfer in the re-reduction of photooxidized reaction-center bacteriochlorophyll was used as Je. deltamue was determined from the intensity of the delayed fluorescence from bacteriochlorophyll. deltamue is composed of the redox potential difference and the electrical potential difference between two electron transfer components. In the steady state under illumination, the flux-to-force ratio is determined by the following relationship: Je = (1--q2)Lee deltamue where q is the "degree of coupling" of electron transfer to proton translocation and Lee is the value of Je/delta-approximately similar e when there is no back pressure by formation of delta approximately muH+ (electrochemical potential difference of H+). The value of (1--q2) Lee increased with increasing pH in the neutral pH range. Uncouplers and ionophores that dissipate delta-approximately muH+ increased Je and decreased deltamue. The effects were more prominent in the lower pH range. Therefore, q must be smaller at higher pH. The coupling is probably tight when redox components are saturated with protons. The experimental results agreed with the theoretical predictions for a system where a hydrogen-translocating component functions as an electron-proton symport carrier.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed2000

Three coupled oscillators as a universal probe of synchronization stability in coupled oscillator arrays

We show that the stability surface that governs the synchronization of a large class of arrays of identical oscillators can be probed with a simple array of just three identical oscillators. Experimentally this implies that it may be possible to probe the synchronization conditions of many arrays all at the same time. In the process of developing a theory of the three-oscillator probe, we also show that several regimes of asymptotic coupling can be derived for the array classes, including the case of large imaginary coupling, which apparently has not been explored.

Journal Article↗
PubMed2002

Coupling-reentrant phase transition, complex hysteretic behavior, and efficiency optimization in coupled phase oscillators submitted to colored flashing potentials.

A recent mean-field analysis of a model consisting of N nonlinear phase oscillators-under the joint influence of global periodic coupling with strength K0 and of local multiplicative and additive noises-has shown a nonequilibrium phase transition towards a broken-symmetry phase exhibiting noise-induced transport, or "ratchet" behavior. In a previous paper we focused on the relationship between the character of the (mean velocity vs load force F) hysteresis loop, the number of "homogeneous" mean-field solutions, and the shape of the stationary mean-field probability distribution function (PDF). Here we assume that the multiplicative noises of the model are Ornstein-Uhlenbeck with common strength Q and self-correlation time tau. By resorting to an effective Markovian approximation, we study the tau dependence of the phase boundary, and that of the line signaling the transition from the "interaction-driven regime" to the "noise-driven regime." We also study-for selected representative points of the K0 vs Q phase diagram-the tau dependence of the transport properties induced by coupling and colored multiplicative noise (including the efficiency epsilon of the mechanical rectification process) and that of the above-mentioned PDF.

Journal Article↗
PubMed2003

Synchronization of coupled rotators: Josephson junction ladders and the locally coupled Kuramoto model.

We show that the resistively shunted junction (RSJ) equations describing a ladder array of overdamped, critical-current disordered Josephson junctions that are current biased along the rungs of the ladder can be mapped onto a Kuramoto model with nearest neighbor, sinusoidal couplings. This result is obtained by an averaging method, in which the fast dynamics of the RSJ equations are integrated out, leaving the dynamics which describe the time scale over which neighboring junctions along the rungs of the ladder phase and frequency synchronize. We quantify the degree of frequency synchronization of the rung junctions by calculating the standard deviation of their time-averaged voltages, sigma(omega), and the phase synchronization is quantified by calculating the time average of the modulus of the Kuramoto order parameter, <|r|>. We test the results of our averaging process by comparing the values of sigma(omega) and <|r|> for the original RSJ equations and our averaged equations. We find excellent agreement for dc bias currents of I(B)/ greater, similar 3, where is the average critical current of the rung junctions, and critical current disorders of up to 10%. We also study the effects of thermal noise on the synchronization properties of the overdamped ladder. Finally, we find that including the effects of junction capacitance can lead to a discontinuous synchronization transition as the strength of the coupling between neighboring junctions is smoothly varied.

Journal Article↗
PubMed2006

Internal signal transmission in one-way coupled excitable system: noise and coupling effects.

We study the spatiotemporal dynamics of a one-way coupled FitzHugh-Nagumo system of twenty neurons, which is subject to external noise at the first neuron. It is shown that noise-induced oscillation (NIO) triggered at the first neuron is propagated along the chain with noise suppression, such that a rather "regular" signal is obtained at the last neuron, which can provide a mechanism for the creation of the informative signal in a neural network. Coherence resonance or coherence biresonance behavior appears in the transmission of NIO at appropriate coupling and the information flow in each neuron can be simultaneously optimized at the optimal value of noise.

Animals↗
PubMed2003

Fine structure of excitons in InAs/GaAs coupled auantum dots: a sensitive test of electronic coupling.

Exciton fine structure in InAs/GaAs coupled quantum dots has been studied by photoluminescence spectroscopy in magnetic fields up to 8 T. Pronounced anticrossings and mixings of optically bright and dark states as functions of magnetic field are seen. A theoretical treatment of the mixing of the excitonic states has been developed, and it traces observed features to structural asymmetries. These results provide direct evidence for coherent coupling of excitons in quantum dot molecules.

Journal Article↗
PubMed1973

Studies on the Energy-coupling Sites of Photophosphorylation: II. Treatment of Chloroplasts with NH(2)OH Plus Ethylenediaminetetraacetate to Inhibit Water Oxidation while Maintaining Energy-coupling Efficiencies.

Artificial electron donors to photosystem II provide an important means for characterizing the newly discovered site of energy coupling near photosystem II. However, water oxidation must be completely abolished, without harming the phosphorylation mechanism, for these donor reactions and the associated phosphorylation to withstand rigorous quantitative analysis. In this paper we have demonstrated that treatment of chloroplasts with hydroxylamine plus EDTA at pH 7.5 in the presence of Mg(2+) followed by washing to remove the amine is a highly reliable technique for this purpose. The decline of the Hill reaction and the coupled phosphorylation during the treatment were carefully followed. No change in the efficiency of phosphorylation (P/e(2) 1.0-1.1) was observed until the reactions became immeasurable. Photosystem I-dependent reactions, such as the transfer of electrons from diaminodurene or reduced 2,6-dichlorophenolindophenol to methylviologen, and the associated phosphorylation were totally unaffected. It is clear that the hydroxylamine treatment is highly specific, with no adverse effect on the mechanism of phosphorylation itself. Benzidine photooxidation via both photosystems II and I in hydroxylamine-treated chloroplasts (electron acceptor, methylviologen; assayed as O(2) uptake) supports phosphorylation with the same efficiency as that observed for the normal Hill reaction (P/e(2) = 1.1). An apparent P/e(2) ratio of 0.6 was computed for the photooxidation of ascorbate.

Journal Article↗
PubMed1981

The Coupling of Electron Flow to ATP Synthesis in Pea and Maize Mesophyll Chloroplasts : I. INTERACTION OF ADENINE NUCLEOTIDES AND ENERGY TRANSFER INHIBITORS WITH THE COUPLING FACTOR COMPLEX.

The rate of nonphosphorylating electron transport (in the absence of ADP and inorganic phosphate) in well-coupled (ATP/2e(-) = 0.9-1.1) maize mesophyll chloroplasts is not modulated by external pH (6.5-8.5), low levels of ADP or ATP, or energy transfer inhibitors, e.g. triphenyltin and Hg(2+) ions. In contrast nonphosphorylating electron flow in pea chloroplasts is sensitive to alterations in medium pH, and to the presence of adenine nucleotides and energy transfer inhibitors in the assay medium. Although ATP is without effect on the rate of basal electron transport in maize chloroplasts, steady-state proton uptake is stimulated 3- to 5-fold by low levels of ATP. These results suggest that differences may exist in the manner in which the coupling factor complex controls proton efflux from the intrathylakoid space in C(3) and C(4) mesophyll chloroplasts.

Journal Article↗
PubMed1990

Kinetic misinterpretation of a coupled enzyme reaction can lead to the assumption of an enzyme-enzyme interaction. The example of 3-phospho-D-glycerate kinase and glyceraldehyde-3-phosphate dehydrogenase couple.

The time course of the conversion of 3-phospho-D-glycerate (GriP) to glyceraldehyde-3-phosphate (GraP) catalyzed by 3-phospho-D-glycerate kinase (GriP kinase) and glyceraldehyde-3-phosphate dehydrogenase (GraPDH) couple has been reinvestigated. The dependence of the steady-state rate on the dehydrogenase concentration is fully compatible with the consecutive nature of the reaction and therefore is not necessarily related to a complex formation of the two enzymes. To derive a Kd value of a bienzyme complex, as was done by Sukhodolets et al. [Sukhodolets, M. V., Muronetz, V. I. & Nagradova, N. K. (1987) Biochem. Int. 15, 373-379], is basically erroneous. In contrast with some previous reports, the maximal activity of GriP kinase is not influenced by the auxiliary enzyme present in the coupled assay system. Thus, no special accelerating effect can be attributed to GraPDH. 1,3-Bisphospho-D-glycerate (GriP2) bound to GriP kinase does not seem to be a substrate for GraPDH, providing evidence against channelling of GriP2 between the two enzymes.

Animals↗
PubMed2000

All classes of calcium channel couple with equal efficiency to exocytosis in rat melanotropes, inducing linear stimulus-secretion coupling.

1. The contribution of low voltage-activated (LVA) T-type Ca2+ channels and four different types of high voltage-activated (HVA) Ca2+ channel to exocytosis, and the relationship between calcium influx and exocytosis during action potentials (APs) were studied in pituitary melanotropes. 2. Selective HVA Ca2+ channel blockers reduced exocytosis, monitored by membrane capacitance measurements, proportional to the reduction in Ca2+ influx. The efficacy of Ca2+ in stimulating exocytosis did not change in the presence of the Ca2+ channel blockers, indicating that all HVA Ca2+ channels act together in stimulating exocytosis. 3. The relationship between Ca2+ influx and exocytosis during the AP was examined using APs recorded from spontaneously active melanotropes as command templates under voltage clamp. Under voltage clamp, multiphasic Ca2+ currents were activated over the entire duration of the APs, i.e. during the rising phase as well as the plateau phase. The maximum amplitude of the Ca2+ current coincided with the peak of the AP. 4. The relationship between Ca2+ entry and exocytosis was linear for the different phases of the AP. Also, the influx of Ca2+ through LVA T-type channels stimulated exocytosis with the same efficacy as through the HVA channels. 5. APs of increasing duration ( approximately 50 to approximately 300 ms) evoked increasing amounts of exocytosis. The number of entering Ca2+ ions and the capacitance change were linearly related to AP duration, resulting in a fixed relationship between Ca2+ entry and exocytosis. 6. The results show that Ca2+ ions, entering a melanotrope, couple with equal strength to exocytosis regardless of the channel type involved. We suggest that the linear relationship between Ca2+ entry and secretion observed under physiological conditions (during APs), results from the equal strength with which LVA and HVA channels in melanotropes couple to exocytosis. This guarantees that secretion takes place over the entire duration of the AP.

Action Potentials↗