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PubMed2000

Protein redox potential measurements based on kinetic analysis with mediated continuous-flow column electrolytic spectroelectrochemical technique. Application to TTQ-containing methylamine dehydrogenase.

Kinetic determination of protein redox potentials with a mediated continuous-flow column electrolytic spectroelectrochemical technique (CFCESET) is described. In this method, the redox state of the mediator is completely regulated by the continuous-flow column electrolysis, and the homogeneous redox reaction between the mediator and a protein sample in the column is monitored spectroscopically at the downstream of the column. The protein/mediator reaction is in the pseudo-first-order kinetics, and then the rate equation is analytically solved. The kinetic analysis provides the protein redox potential as well as the homogeneous rate constant. In the kinetic measurements, equilibration of the system within the column is not required, which allows the use of increased kinds of mediators. This method was successfully applied to quinoprotein methylamine dehydrogenase containing tryptophan tryptophylquinone (TTQ) as a prosthetic group. The kinetic aspect is also valuable for the thermodynamic analysis with the mediated CFCESET. The half-life time of the kinetics can be utilized to optimize the system for the attainment of the equilibrated state within the column and can provide the assurance that the system is in equilibrium.

Electrochemistry↗
PubMed2005

Atomic orbitals in molecules: general electronegativity and improvement of Mulliken population analysis.

An approach of atomic orbitals in molecules (AOIM) has been developed to study the atomic properties in molecules, in which the molecular orbitals are expressed in terms of the optimized minimal atomic orbitals. The atomic electronegativities are calculated using Pauling's electronegativity of free atom and are employed to find the electronegativity equilibrium in molecules and to describe the amphoteric properties of the transition metals from the groups 4 to 10. AOIM can also improve the numerical stability and accuracy of the original Mulliken population analysis.

Electrons↗
PubMed2005

Mechanism of 1,4,5,8-naphthalene tetracarboxylic acid dianhydride hydrolysis and formation in aqueous solution.

The study of highly conjugated, carbonyl-containing molecules such as 1,4,5,8-naphthalene tetracarboxylic dianhydride, III, is of interest since reactivity differences and transmission of electronic effects through the conjugated framework can be evidenced. The kinetics of hydrolysis of III in aqueous solution were determined from 5 M acid to pH 10. In basic solution hydrolysis of III yields, sequentially, 1,4,5,8-naphthalene diacid monoanhydride, II, and 1,4,5,8-naphthalene tetracarboxylic acid, I. The second order rate constant for alkaline hydrolysis is 200 fold higher for the first ring opening. The water-catalyzed hydrolysis of III yields a pH-dependent mixture of ionic forms of I and II. The rate constant for water-catalyzed hydrolysis of III is 25 fold higher than that for II. In concentrated acid the rates for reaching equilibrium (I, II and III) increase and III is the major product. The pK(a)s of I (3.24, 5.13 and 6.25) and II (3.05, 5.90) were determined by potentiometric, fluorescence and UV spectroscopy titrations and by quantitative fit of the kinetic and equilibrium data. The apparent, pH-dependent, equilibrium constants, K(EqII), for anhydride formation between I and II were obtained from the UV spectra. The quantitative fit of kinetic and equilibrium data are consistent with the assumption that anhydride formation only proceeds with the fully protonated species for both I and II and permitted the estimation of the equilibrium constants for anhydride formation, K(EqII). The value of K(EqII) (I <==> II) between pH 1 and 6 was ca. 5. Geometry optimization calculations in the gas phase of the reactions of III in alkaline, neutral and acid conditions, at the DFT level of theory, gave electronic distributions that were qualitatively consistent with the experimental results.

Gases↗
PubMed1998

[Tissue oxygenation: physiological and pathophysiologic aspects in intensive care].

Continuous oxygen supply to the tissues is one of the many important factors in intensive care. However, as a basic requirement for the structure and function of higher developed organisms energy production by oxydative metabolism is of outstanding importance, because there is no significant storage of energy and anaerobic metabolism is insufficient. The determinants of oxygen supply--blood flow and oxygen content--are well known. The system stands out for its extensive ability to compensate imbalances. Nevertheless one has to bear in mind also rather trivial disturbances like insufficient respiration and hypovolemia. Absolute values of global parameters, however, provide no information on the oxygen supply of individual organs that are variably susceptible to hypoxia. Regional perfusion and tissue respiration are influenced by various factors. Together with systemic components the physiologic oxygen transport along the oxygen cascade follows demand. Regardless of their position on the oxygen cascade malfunctions of oxygenation impair first the function and eventually the structure of the tissues. An utilisation block on the cellular level can prevent sufficient energy production despite optimized oxygen supply, the damage of reperfusion can intensify the effects of hypoxia. Typical haemodynamic patterns follow the tissue hypoxia. For maintaining an equilibrium between oxygen demand and supply it is important that oxygen consumption is also influenced by numerous factors. Only when an imbalance between oxygen supply and demand--an oxygen debt--is realized at an early stage, the critically ill patient can be saved from irreversible damage. In the field of intensive care the frequently latent tissue hypoxia is often a result of the chronic oxygen debt of individual, particularly vulnerable organs. Considering those aspects the intestinal mucosa is particularly suited for the monitoring of tissue oxygenation in the critically ill patient.

Critical Care↗
PubMed1999

Energy transduction of isothermal ratchets: generic aspects and specific examples close to and far from equilibrium.

We study the energetics of isothermal ratchets which are driven by a chemical reaction between two states, and operate in contact with a single heat bath of constant temperature. We discuss generic aspects of energy transduction such as Onsager relations in the linear response regime as well as the efficiency and dissipation close to and far from equilibrium. In the linear response regime where the system operates reversibly, the efficiency is in general nonzero. Studying the properties for specific examples of energy landscapes and transitions, we observe in the linear response regime that the efficiency can have a maximum as a function of temperature. Far from equilibrium in the fully irreversible regime, we find a maximum of the efficiency with values larger than in the linear regime for an optimal choice of the chemical driving force. We show that the corresponding efficiencies can be of the order of 50%. A simple analytic argument allows us to estimate the efficiency in this irreversible regime for small external forces.

Energy Metabolism↗
PubMed2005

Anatomy, function, and rehabilitation of the popliteus musculotendinous complex.

We present a clinical commentary of existing evidence regarding popliteus musculotendinous complex anatomy, biomechanics, muscle activation, and kinesthesia as they relate to functional knee joint rehabilitation. The popliteus appears to act as a dynamic guidance system for monitoring and controlling subtle transverse- and frontal-plane knee joint movements, controlling anterior-posterior lateral meniscus movement, unlocking and internally rotating the knee joint (tibia) during flexion initiation, assisting with 3-dimensional dynamic lower extremity postural stability during single-leg stance, preventing forward femoral dislocation on the tibia during flexed-knee stance, and providing for postural equilibrium adjustments during standing. These functions may be most important during mid-range knee flexion when capsuloligamentous struCtures are unable to function optimally. Because the popliteus musculotendinous complex has attachments that approximate the borders of both collateral ligaments, it has the potential for providing instantaneous 3-dimensional kinesthetic feedback of both medial and lateral tibiofemoral joint compartment function. Enhanced popliteus function as a kinesthetic knee joint monitor acting in synergy with dynamic hip muscular control of femoral internal rotation and adduction, and ankle subtalar muscular control of tibial abduction-external rotation or adduction-internal rotation, may help to prevent athletic knee joint injuries and facilitate recovery during rehabilitation by assisting the primary sagittal plane dynamic knee joint stabilization provided by the quadriceps femoris, hamstrings, and gastrocnemius.

Biomechanical Phenomena↗
PubMed1999

Asymmetric synthesis of chiral amines with omega-transaminase.

The asymmetric synthesis of chiral amines using prochiral ketones was carried out with (S)-specific omega-transaminase (omega-TA) from Vibrio fluvialis JS17. This reaction is inhibited severely by both products, (S)-amine and deaminated ketone. In addition, thermodynamic equilibrium strongly favored the reverse reaction. L-Alanine proved to be the best amino donor based on easy removal of the products. Optimal pH of the reactions with both whole cells and cell-free extract was 7. Amino acceptor reactivities of ketone substrates and reaction profiles of the asymmetric synthesis showed that the initial rate as well as the reaction yield were lower when the resulting (S)-amine from a prochiral ketone substrate was a more reactive amino donor. The yield could be increased dramatically by removing pyruvate, which is a more inhibitory product than (S)-alpha-methylbenzylamine [(S)-alpha-MBA] when acetophenone and L-alanine are used as an amino acceptor and donor, respectively. The removal of pyruvate was carried out by incorporating lactate dehydrogenase (LDH) in cell-free extract or by using whole cells. The whole cell reaction yielded a much better result. When 25 mM benzylacetone and 30 mM acetophenone were used as an amino acceptor with 300 mM L-alanine, 90.2% and 92.1% of the reaction yields after 1 day were obtained with whole cells, respectively. Enantiomeric excesses of both (S)-alpha-MBA and (S)-1-methyl-3-phenylpropylamine [(S)-MPPA] were all above 99%.

Alanine↗
PubMed1976

Studies on heart phosphofructokinase. Use of fructose 6-sulfate as an alternative substrate to study the mechanism of action and active site specificity.

Fructose 6-sulfate was synthesized by direct sulfurylation of fructose and was isolated by two selective steps: (a) conversion of the 6-sulfuryl ester to fructose 1-phosphate-6-sulfate with phosphofructokinase; (b) conversion of fructose 1-phosphate-6-sulfate to fructose 6-sulfate by fructose-1,6-diphosphatase. Utilizing crystalline sheep heart phosphofructokinase, kinetic studies with the alternative substrate were carried out at pH 8.2 which is optimal for nonallosteric kinetics. The data are consistent with an ordered addition of the two substrates with the first, MgATP, being at thermodynamic equilibrium. The Vmax and Km obtained with fructose 6-sulfate were 0.03- and 100-fold, respectively, that obtained with the natural substrate. The study suggests that the divalent phosphoryl moiety is intimately involved in the active site conformation. Identification of the product of the reaction, fructose 1-phosphate-6-sulfate, was confirmed through studies with aldolase, fructose-1,6-diphosphatase, and by 31P NMR. The utilization of fructose 6-sulfate as a substrate by yeast glucose-6-phosphate isomerase could not be demonstrated.

Animals↗
PubMed1993

[Radionuclide ventriculography for evaluating left ventricular myocardial contractility in patients with implanted pacemaker].

An EKC-500 pacemaker was implanted in 16 patients with coronary heart disease (CHD) and 14 idiopathic conduction disturbance for complete atrioventricular block. After surgery, the patients underwent equilibrium radionuclide ventriculography by using a nuclear stethoscope at rest and during exercise at different stimulation rates with the aim of choosing their optimal values. It was established that patients with idiopathic conduction disturbances showed improved left ventricular contractility at all stimulation rates and their optimal values ranged 60-70 per minute. In patients with CHD, the stimulation rate of 60 impulses/min was optimal at rest, and with this, exercise resulted in a significant deterioration of myocardial contractility, but only the stimulation rate of 80 impulses/min led to a slight improvement, which was due to accessory mechanisms of contractility enhancement. The peak ejection rate was the most sensitive to progressive myocardial dysfunction, yet the basic contractility index was the mean ejection rate.

Arrhythmias, Cardiac↗
PubMed1990

Kinetics of antagonism at histamine-H1 receptors in isolated rabbit arteries.

Kinetics of antagonist-induced decrease of histamine-H1 receptor-mediated steady-state responses in isolated rabbit arteries were studied in the presence of histamine-H2 receptor antagonist famotidine. Data were fitted using a model which describes competition kinetics at the receptor level. Estimated rate and equilibrium constants were evaluated for their dependence on tissue, agonist and antagonist concentrations, using (+)-brompheniramine as antagonist. In large arteries (thoracic and arcus aorta), rate constants were observed to be modified by agonist and/or antagonist concentrations, suggesting a diffusion-controlled process. In relatively small (common carotid and iliac) arteries, estimated equilibrium constants (and consequently the rate constants) were found to diverge despite the invariance of equilibration times between arteries, leading us to include the effects of spare receptors in our evaluation. A model describing the effects of receptor reserve on the estimated equilibrium dissociation constant was developed and stimulated and the results then compared with those that had been experimentally estimated. The reserve hypothesis was experimentally verified in common iliac artery (where EC50 much less than KA) using the irreversible antagonist phenoxybenzamine. A rationalized rule for the optimization of experimental design for in-vitro disequilibrium-competition experiments was proposed. Common carotic artery was found to be favorable for the present design in view of its reserve properties. In addition, competition reaction seems to be the rate-determining step in this artery. Rate and equilibrium constants of mepyramine, (+)-brompheniramine, diphenhydramine and antazoline were therefore determined in the common carotid artery and were compared with those obtained from independent experiments. Results suggest that the estimated parameters reflect drug-receptor interaction.

Animals↗
PubMed2006

Estimation of serotonin transporter parameters with 11C-DASB in healthy humans: reproducibility and comparison of methods.

UNLABELLED: The aim of the present study was to define the optimal analytic method to derive accurate and reliable serotonin transporter (SERT) receptor parameters with (11)C-3-amino-4-(2-[(dimethylamino)methyl]phenylthio)benzonitrile ((11)C-DASB). METHODS: Nine healthy subjects (5 females, 4 males) underwent two (11)C-DASB PET scans on the same day. Five analytic methods were used to estimate binding parameters in 10 brain regions: compartmental modeling with 1- and 2-tissue compartment models (1TC and 2TC), data-driven estimation of parametric images based on compartmental theory (DEPICT) analysis, graphical analysis, and the simplified reference tissue model (SRTM). Two variations in the fitting procedure of the SRTM method were evaluated: nonlinear optimization and basis function approach. The test/retest variability (VAR) and intraclass correlation coefficient (ICC or reliability) were assessed for 3 outcome measures: distribution volume (V(T)), binding potential (BP), and specific to nonspecific equilibrium partition coefficient (V(3)''). RESULTS: All methods gave similar values across all regions. The variability of V(T) was excellent (< or =10%) in all regions, for the 1TC, 2TC, DEPICT, and graphical approaches. The variability of BP and V(3)'' was good in regions of high SERT density and poorer in regions of moderate and lower densities. The ICC of all 3 outcome measures was excellent in all regions. The basis function implementation of SRTM demonstrated improved reliability compared with nonlinear optimization, particularly in moderate and low-binding regions. CONCLUSION: The results of this study indicate that (11)C-DASB can be used to measure SERT parameters with high reliability and low variability in receptor-rich regions of the brain, with somewhat less reliability and increased variability in regions of moderate SERT density and poor reproducibility in low-density regions.

Adult↗
PubMed1977

Evolution of enzyme catalytic power. Characteristics of optimal catalysis evaluated for the simplest plausible kinetic model.

1. Evolutionary changes in the structure of an enzyme that provide an increase in its K(m) value are considered. Provided that K(m) increases as a result of increases in the forward rate constants of the catalysis relative to the reverse rate constants, the enzyme catalyses the conversion of a fixed concentration of its substrate more rapidly when its structure provides that K(m)>[S] than when K(m)<[S]. 2. Catalytic efficiency of enzymes is discussed in terms of the simplest plausible model, the Haldane [(1930) Enzymes, Longmans, London] reversible three-step model: [Formula: see text] The rate equation for the forward reaction of this model (formation of P) may be written in the simple form: [Formula: see text] K(eq.) is the equilibrium constant (=[P](eq.)/[S](eq.)), and k(cat.)=V/[E](T), where [E](T) is the total enzyme concentration. 3. To assess the effectiveness of an enzyme, it is necessary only to determine the extent to which the constraints of a particular kinetic mechanism permit v(2) (v when K(m)>>[S]) to approach v(d) (the diffusion-limited rate). 4. The value of the optimal rate of catalysis (v(opt.), the maximal value of v(2)) is dictated by the equilibrium constant for the reaction, K(eq.); v(2)=v(d)/a, where [Formula: see text] when k(+1) is assumed equal to k(-3), and v(opt.)=v(d)/a(min.). When K(eq.)>/=1, it is necessary that k(+2)>>k(-1) for a to take its minimum value, a(min.); when K(eq.)<<1, it is necessary only that k(+2)>>K(eq.).k(-1), i.e. a can equal a(min.) even if k(+2) >1, v(opt.)=v(d); when K(eq.)=1, v(opt.)=v(d)/2, and when K(eq.)<<1, v(opt.)=K(eq.).v(d). 5. The analysis, together with predicted effects of evolutionary pressure, suggests that in practice the rates of the fastest enzyme-catalysed freely reversible reactions might be expected to be lower than the value of k(+1)[E](T)[S] by about an order of magnitude, particularly if K(eq.)<1. 6. The existing literature suggests that, in general, appropriate values of K(m) have evolved for the provision of high rates of catalysis but that many values of k(cat.) are not large enough to provide optimal rates of catalysis unless the value of k(+1)in vivo is lower than its value in free solution.

Biological Evolution↗
PubMed2002

Numerical experiments on long-time orthodontic tooth movement.

In orthodontic treatment, teeth are moved by the use of specific force systems. The force system used depends on the patient's orthodontic situation characterized by the geometry of the tooth and the surrounding alveolar bone, which defines the position of the center of resistance. Therefore, the simulation of bone remodeling could be helpful for the treatment strategy. In this study, the optimal force system for bodily movement of a single-root tooth, with an orthodontic bracket attached, was determined. This was achieved by the use of the numerical finite element method, including a distinct mechanical bone-remodeling algorithm. This algorithm works with equilibrium iterations separated in 2 calculation steps. Furthermore, a parametric 3-dimensional finite element model, which allows modifications in the root length and its diameter, is described. For different geometries, the ideal moment-by-force ratios that induce a bodily movement were determined. The knowledge of root geometry is important in defining an optimal force system.

Algorithms↗
PubMed2004

Maximization principles and daisyworld.

We investigate whether the equilibrium time-averaged state of a self-organizing system with many internal degrees of freedom, 2D-daisyworld, can be described by optimizing a single quantity. Unlike physical systems where a principle of maximum energy production has been observed, daisyworld follows evolutionary dynamics rather than Hamiltonian dynamics. We find that this is sufficient to invalidate the maximum entropy production principle, finding instead a different principle, that the system self-organizes to a state which maximizes the amount of life.

Biological Evolution↗
PubMed2001

Surface-enhanced Raman scattering on uniform platinum-group overlayers: preparation by redox replacement of underpotential-deposited metals on gold.

The preparation of Pt-group metal films on roughened gold electrodes by utilizing spontaneous redox replacement of an underpotential-deposited (upd) copper or lead monolayer with a Pt-group metal cation solute is described. The resulting films display intense surface-enhanced Raman scattering (SERS) for adsorbates bound to the overlayer and free from substrate interferences. This strategy provides a useful alternative, at least for platinum, to the constant-current electrodeposition method commonly utilized to prepare SERS-active Pt-group metal films (Zou, S.; Weaver, M. J. Anal. Chem. 1988, 70. 2387). Similarly to related earlier studies, the film uniformity (specifically, the absence or otherwise of residual Au "pinhole" sites) was tested by employing carbon monoxide, and also ethylene, as "probe" chemisorbates, since they yield vibrational frequencies on Au that are blue-shifted from the corresponding bands for adsorbate bound to Pt-group metal sites. While a single redox replacement of upd Cu with Pt(IV) yielded incomplete surface coverage, as expected, the use of multiple (up to eight) replacement cycles produced Pt films displaying remarkably intense CO vibrational bands as well as apparently "pinhole-free" properties, although such imperfections were detected with the ethylene probe. A single upd Cu replacement with Pt(II), however, yielded a remarkably uniform Pt layer, as indicated by pinhole-free characteristics using both the CO and ethylene probes along with the voltammetric behavior. The use of additional redox replacement cycles yielded marked progressive attenuation in the SERS signals. Comparable, although less optimal, SERS behavior was obtained for Pd films prepared similarly from Pd(II). The value of the strategy for exploring catalytic as well as equilibrium adsorptive chemistry on Pt surfaces is also illustrated.

Journal Article↗
PubMed1983

Mechanism of modulation of dopamine beta-monooxygenase by pH and fumarate as deduced from initial rate and primary deuterium isotope effect studies.

Dopamine beta-monooxygenase catalyzes a reaction in which 2 mol of protons are consumed for each turnover of substrate. Studies of the pH dependence of initial rate parameters (Vmax and Vmax/Km) and their primary hydrogen isotope effects show that at least two ionizable residues are involved in catalysis. One residue (B1, pK = 5.6-5.8) must be protonated prior to the carbon-hydrogen bond cleavage step, implying a role for general-acid catalysis in substrate activation. A second protonated residue (B2, pK = 5.2-5.4) facilitates, but is not required for, product release. Recent measurement of the intrinsic isotope effect for dopamine beta-monoxygenase [Miller, S. M., & Klinman, J. P. (1983) Biochemistry (preceding paper in this issue)] allows an analysis of the pH dependence of rate constant ratios and in selected instances individual rate constants. We demonstrate large changes in the rate-determining step as well as an unprecedented inversion in the kinetic order of substrate release from ternary complex over an interval of 2 pH units. Previously, fumarate has been used in dopamine beta-monooxygenase assays because of its property of enzyme activation. Studies of the pH behavior in the presence of saturating concentrations of fumarate have shown two causes of the activation: (i) fumarate perturbs the pK of B1 to pK = 6.6-6.8 such that the residue remains protonated and the enzyme optimally active over a wider pH range; (ii) fumarate decreases the rate of dopamine release from the ternary enzyme-substrate complex, increasing the equilibrium association constant for dopamine binding. Both effects are consistent with a simple electrostatic stabilization of bound cationic charges by the dianionic form of fumarate.

Animals↗
PubMed2005

Reaction coordinates and rates from transition paths.

The molecular mechanism of a reaction in solution is reflected in its transition-state ensemble and transition paths. We use a Bayesian formula relating the equilibrium and transition-path ensembles to identify transition states, rank reaction coordinates, and estimate rate coefficients. We also introduce a variational procedure to optimize reaction coordinates. The theory is illustrated with applications to protein folding and the dipole reorientation of an ordered water chain inside a carbon nanotube. To describe the folding of a simple model of a three-helix bundle protein, we variationally optimize the weights of a projection onto the matrix of native and nonnative amino acid contacts. The resulting one-dimensional reaction coordinate captures the folding transition state, with formation and packing of helix 2 and 3 constituting the bottleneck for folding.

Adenosine Triphosphate↗
PubMed1984

Difference in radiosensitivity of valyl-tRNA synthetases isolated from chick embryo liver and brain.

The sensitivity in vitro against gamma-radiation of valyl-tRNA synthetase (VRS) from chick embryo brain proved to be higher than that of liver VRS. In order to study this phenomenon properties of VRS isolated from both organs were compared. Both enzymes have the same molecular weight (Mr = 110 000) determined by equilibrium sedimentation and by gel filtration. Electrophoresis on polyacrylamide gel in the presence of sodium dodecyl sulphate showed no evidence for subunit structure. The optimal reaction conditions in valyl-tRNA formation were found to be the same, except the pH values. Km values of the reactions were also similar. Both enzymes reacted with the tRNAs isolated from the other organ. The stability during storage of the liver VRS was higher than that of the brain VRS. In the brain VRS molecule one buried and eleven free SH groups could be detected and divided into three classes with different reactivities. In 1 mol of liver VRS one buried and nine free thiol groups were determined and these could be divided only into two classes. These observations suggest the existence of two VRS isoenzymes with different radiosensitivities: the more sensitive occurs mainly in brain and the less sensitive mainly in the liver of chick embryo.

Amino Acyl-tRNA Synthetases↗