Neurocognitive functions in patients with hepatitis C infection.

Background And Purpose: With improving treatment options, more attention is being paid to the neurocognitive symptoms related to hepatitis C infection (HCI). While HCI-related neurocognitive impairments are frequently subclinical, they can influence patients' quality of life and fitness to work. Objective - The aim of this study was to assess HCI patients' neurocognitive functions and explore the correlations between disease variables and neurocognitive symptoms.

Effect of hepatitis C infection on the quality of life.

Purpose: To assess the quality of life (QoL) of patients with hepatitis C infection (HCI) and its correlations with demographic and clinical variables.

Design And Methods: QoL and depressive symptoms were evaluated with the validated rating instruments of the 36-item short form (SF-36) generic health survey and the second version of the self-rated Beck depression inventory (BDI-II) in a cross-sectional design and correlated with basic demographic and clinical variables, including the Fibroscan score, which indicates the severity of liver impairment.

Findings: A cohort of 60 HCI patients who participated in the study scored lower than the general population on all domains of the SF-36.

Substrate binding properties of L-glycerol-3-phosphate dehydrogenase in isolated liver mitochondria of hyperthyroid rats.

In isolated, intact liver mitochondria from hyperthyroid rats, the L-glycerol-3-phosphate binding site(s) of the L-glycerol-3-phosphate dehydrogenase was (were) found to be influenced by the nature of the electron acceptor, as well as by the pH and the presence of calcium ions. With the hydrophobic electron acceptor menadione a single L-glycerol-3-phosphate binding site was detected kinetically at bulk pH values between 6.5 and 9.

Double inhibition of L-threonine dehydratase by aminothiols.

The inhibition of highly purified rat liver L-threonine dehydratase (L-threonine hydro-lyase (deaminating), EC 4.2.1.

Transient-time analysis of substrate-channelling in interacting enzyme systems.

The kinetics of dynamically interacting enzyme systems is examined, in the light of increasing evidence attesting to the widespread occurrence of this mode of organization in vivo. The transient time, a key phenomenological parameter for the coupled reaction, is expressed as a function of the lifetime of the intermediate substrate. The relationships between the transient time and the pseudo-first-order rate constants for the coupled reaction by the complexed and uncomplexed enzyme species are indicative of the mechanism of intermediate transfer ('channelling').

Coupled enzymatic reactions measured in a single protein crystal from myogen A.

Pairwise coupled reactions of fructose-1,6-bisphosphate aldolase and sn-glycerol-3-phosphate dehydrogenase, 3-phosphoglycerate kinase and D-glyceraldehyde-3-phosphate dehydrogenase, triosephosphate isomerase and sn-glycerol-3-phosphate dehydrogenase have been detected by microspectrophotometry in single crystals obtained from myogen A in the presence of polyethylene glycol. Microspectrophotometric measurements with polarized light demonstrate that the protein molecules are oriented and that NADH is bound with a definite orientation to the dehydrogenases within the crystal.

The perfection of substrate-channelling in interacting enzyme systems: energetics and evolution.

Some implications of substrate channelling in interacting enzyme systems are considered, with regard to the energetics and evolution of enzyme action. The transient time, a key analytical parameter relating to the phenomenon of channelling, is the basis of our kinetic study. Bounds on the kinetics of multienzyme complexes are established using (apparent) rate constants emanating from the transient-time formulation of coupled reactions.

Kinetic evidence for a reversible isomerization of pig muscle glyceraldehyde-3-phosphate dehydrogenase in its crystallization medium.

Ammonium sulfate, a typical component of crystallization media of proteins, stabilizes an inactive conformation of pig muscle glyceraldehyde-3-phosphate dehydrogenase. In fact, in the presence of ammonium sulfate the reconstitution of the catalytically active holoenzyme from the apoenzyme and NAD is not instantaneous, as in the case of enzymes from Bacillus stearothermophilus and the Mediterranean lobster Palinurus vulgaris. With pig muscle enzyme, at pH 6.

The control of cell metabolism for homogeneous vs. heterogeneous enzyme systems.

Metabolic control theories, based on such parameters as "elasticity coefficients" and "flux-control coefficients", have emerged in recent years. These offer a potentially unifying, holistic paradigm for understanding the regulation of cell metabolism. Much of the foundation relies on the supposition that the system is a homogeneous bulk-phase solution of individual enzymes.

A kinetic method for distinguishing whether an enzyme has one or two active sites for two different substrates. Rat liver L-threonine dehydratase has a single active site for threonine and serine.

We have elaborated a kinetic method which allows us to evaluate whether a Michaelis-Menten-type enzyme acting on two different substrates has one or two active sites. This method has been used with the rat liver L-threonine dehydratase, which catalyzes the dehydrative deamination of both serine and threonine. The experimental data can be fitted to the theoretical plot obtained for the case of a single active site.

Microenvironment of the enzyme-bound NADH is different in lobster and pig muscle glyceraldehyde-3-phosphate dehydrogenase microcrystals.

Two possible consequences of crystal lattice formation were studied with glyceraldehyde-3-phosphate dehydrogenases isolated from lobster (Palinurus vulgaris) and pig muscle: changes in the microenvironment of the NADH-binding site as detected by fluorescence polarization, and differences in the maximal activities of the microcrystalline enzymes as compared to those in solution. In solution practically no difference was found between the polarization values of the enzyme-NADH and the catalytic intermediate 3-phosphoglyceroyl-enzyme-NADH complexes whether with lobster or with pig enzyme. In microcrystalline state a similar effect was found with the lobster enzyme.

Two rules of enzyme kinetics for reversible Michaelis-Menten mechanisms.

In a Michaelis-Menten type reversible enzyme reaction (one substrate, one product) the rapid equilibrium kinetics in one direction excludes rapid equilibrium in the reverse direction. If rapid equilibrium functions in any direction, in the reverse reaction van Slyke type 'kinetic constant' appears in the rate equation independently of whether steady state is reached in finite time or the final equilibrium is attained at t = infinity. If the reaction proceeds in one direction with rapid equilibrium and in the reverse direction with steady-state kinetics, the thermodynamic equilibrium of the reaction determines that a higher equilibrium concentration of product (or substrate) can be reached only with steady-state kinetics.

On the NADPH dependent reaction of cytoplasmic sn-glycerol-3-phosphate dehydrogenase.

Cytoplasmic sn-glycerol-3-phosphate dehydrogenase (EC. 1.1.

Determination of Michaelis-Menten parameters from initial velocity measurements using unstable substrate.

By initial velocity measurements and two different methods of plotting the experimental data, the Km and Vmax of enzyme action and the first-order rate constant of substrate decomposition can be determined simultaneously under the same conditions. This method permits the determination of Km and Vmax even if the presence of the enzyme (or any impurity in the solutions used) influences the rate of substrate decomposition. The theoretical treatment was proved by determining the Michaelis-Menten parameters of D-glyceraldehyde-3-phosphate dehydrogenase and the first-order rate constant of hydrolysis of the unstable substrate, bisphosphoglycerate.

Stability, heat stability and heat sensitivity of proteins: thermodynamic considerations.

The heat sensitivity and stability of a protein should be characterized by the Arrhenius parameters of the irreversible denaturation. The terms "thermostability" or "activation enthalpy" and "activation entropy" of denaturation as "thermodynamic parameters of protein stability" are misleading. The terms "measure of heat sensitivity" and "measure of stability" should be used as comparative data for protein structure.

The evolution of enzyme kinetic power.

Evolution of the kinetic potential of enzyme reactions is discussed. Quantitative assessment of the evolution of enzyme action has usually focused on optimization of the parametric ratio kcat./Km, which is the apparent second-order rate constant for the reaction of free substrate with free enzyme to give product.

Errors in the evaluation of Arrhenius and van't Hoff plots.

Errors in the numerical values of activation or normal enthalpies, entropies and free enthalpies calculated from Arrhenius or van't Hoff plots, respectively, are due to the neglect of equidimensionality in equations, or to inappropriate approximations. The logarithmization of dimensioned quantities should be avoided, which demands the use of relative concentrations if a change in mole number occurs in the reaction. The application of the Arrhenius plot to enzymic reactions by using Vmax.

Homologous partial sequences in dehydrogenases.

Such details of the primary structure were sought that are common in all dehydrogenases of known amino acid sequence. Twenty-six sequences of eight kinds of dehydrogenase (D-glyceraldehyde-3-phosphate dehydrogenase, alcohol dehydrogenase, lactate dehydrogenase, glutamate dehydrogenase, glycerol-3-phosphate dehydrogenase, ribitol dehydrogenase, L-hydroxyacyl-CoA dehydrogenase and homoserine dehydrogenase) have been compared by the aid of the artificial intelligence language Prolog, the amino acids being classified into groups according to their chemical properties, and alpha-helix or beta-sheet-forming abilities. We found tetrapeptides that occurred in all dehydrogenases examined.

Kinetics of coupled reactions catalyzed by aspartate aminotransferase and glutamate dehydrogenase.

Liver mitochondrial aspartate aminotransferase and glutamate dehydrogenase catalyze following sequence of reactions: see formula in text. In the presence of a slight excess of dehydrogenase, the time course of NADPH oxidation resulting from the overall reaction goes through a lag phase and reaches a linear phase. The slopes of the linear part of this curve is a linear function of transaminase concentration.