PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “molecular kinetics”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1979

[Molecular-kinetic parameters of thiamine enzymes and the mechanism of antivitamin action of hydroxythiamine in animal organisms].

The molecula-kinetic parameters (Km, Ki) of three thiamine enzymes, e. g. thiamine pyrophosphokinase (EC 2.7.6.2), pyruvate dehydrogenase (EC 1.2.4.1) and transketolase (EC 2.2.1.1) with respect to the effects of the thiamine antimetabolite hydroxythiamine in the whole animal organism have been compared. It has been shown that only the first two enzymes, which interact competitively with the vitamin, antivitamin or their pyrophosphate ethers, obey the kinetic parameters obtained for the purified enzymes in vitro. The anticoenzymic effect of hydroxythiamine pyrophosphate with respect to transketolase is not observed in vivo at maximal concentration of the anticoenzyme in tissues due to the absence of competitive interactions with thiamine pyrophosphate. The incorporation of the true and false coenzymes into transketolase occurs only during de novo transketolase synthesis (the apoform is absent in tissues, with the exception of erythrocytes) and proceeds slowly with a half-life time equal to 24--30 hrs. After a single injection of hydroxythiamine at a large dose (70--400 mg/kg) the maximal inhibition of the transketolase activity in tissues (liver, heart, kidney, muscle, spleen, lungs adrenal grands) manifests itself by the 48th--72nd hour, when the concentration of free hydroxythiamine and its pyrophosphate is minimal and the whole anticoenzyme is tightly bound to the protein, forming the false holoenzyme. The use of hydroxythiamine for inhibition of pyruvate dehydrogenase or transketolase in animal organism is discussed.

Animals↗
PubMed1978

Glucose-6-phosphate dehydrogenase of Anabaena sp. Kinetic and molecular properties.

The kinetic and molecular properties of cyanobacterial glucose-6-phosphate dehydrogenase, partly purified from Anabaena sp. ATCC 27893, show that it undergoes relatively slow, reversible transitions between different aggregation states which differ in catalytic activity. Sucrose gradient centrifugation and polyacrylamide gel electrophoresis reveal three pincipal forms, with approximate molecular weights of 120 000 (M1), 240 000 (M2) and 345 000 (M3). The relative catalytic activities are: M1 less than M2 less than M3. In concentrated solutions of the enzyme, the equilibrium favors the more active, oligomeric forms. Dilution in the absence of effectors shifts the equilibrium in favor of the M1 form, with a marked diminution of catalytic activity. This transition is prevented by a substrate, glucose-6-phosphate, and also by glutamine. The other substrate, nicotinamide adenine dinucleotide phosphate (NADP+), and (in crude cell-free extracts) ribulose-1,5-diphosphate are negative effectors, which tend to maintain the enzyme in the M1 form. The equilibrium state between different forms of the enzyme is also strongly dependent on hydrogen ion concentration. Although the optimal pH for catalytic activity is 7.4, dissociation to the hypoactive M1 form is favored at pH values above 7; a pH of 6.5 is optimal for maintenance of the enzyme in the active state. Reduced nicotamide adenine dinucleotide phosphate (NADPH) and adenosine 5'-triphosphate (ATP), inhibit catalytic activity, but do not significantly affect the equilibrium state. The relevance of these findings to the regulation of enzyme activity in vivo is discussed.

Adenosine Triphosphate↗
PubMed1979

AMP deaminase from baker's yeast. Kinetic and molecular properties.

The kinetic and molecular properties of AMP deaminase [AMP aminohydrolase, EC 3.5.4.6] purified from baker's yeast (saccharomyces cerevisiae) were investigated. The enzyme was activated by ATP and dATP, but inhibited by Pi and GTP in an allosteric manner. Alkali metal ions and alkaline earth metal ions activated the enzyme to various extent. Kinetic negative cooperativity was observed in the binding of nucleoside triphosphates. Kinetic analysis showed that the number of interaction sites for AMP (substrate) and Pi (inhibitor) is two each per enzyme molecule. The molecular weight of the native enzyme was estimated to be 360,000 by sedimentation equilibrium studies. On polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, the enzyme gave a single polypeptide band with a molecular weight of 83,000, suggesting that the native enzyme has a tetrameric structure. Baker's yeast AMP deaminase was concluded to consist of two "promoter" units which each consist of two polypeptide chains with identical molecular weight.

AMP Deaminase↗
PubMed1979

A fluorescence stopped-flow study on troponin labeled with N-ethyl maleimide and N-(p-(2-benzimidazolyl)phenyl) maleimide.

The kinetics of the conformational change of the troponin-C (TN-C) subunit in N-(p-(2-benzimidazolyl)phenyl) maleimide (BIPM)-N-ethyl maleimide (NEM)-labeled troponin induced by calcium binding or removal were studied with the fluorescence stopped-flow method. The kinetic process of the conformational change was biphasic, the rate constants of the two phases were determined as a function of the free calcium ion concentration of the protein solution. The kinetic behaviour of the conformational change of TN-C in BIPM-NEM-labeled troponin was explained by a simple molecular kinetic mechanism: (Formula: see text) This molecular kinetic mechanism is different from that of the isolated TN-C which we found in the previous work (1). That is, formation of a complex of TN-C with troponin-I (TN-I) and troponin-T (TN-T) modifies the molecular kinetic mechanism of the conformational change of TN-C.

Animals↗
PubMed1978

Phosphoenolpyruvate carboxylase from the crassulacean plant Bryophyllum fedtschenkoi Hamet et Perrier. Purification, molecular and kinetic properties.

Phosphoenolpyruvate carboxylase from the Crassulacean plant Bryophyllum fedtschenkoi has been purified to homogenetity by DEAE-cellulose treatment, (NH4)2SO4 fractionation,, and chromatography on DEAE-cellulose and hydroxyapatite. Poly(ethylene glycol) is required in the extraction medium to obtain maximum enzyme activity. The purified enzyme has a specific activity of about 26 units/mg of protein at 25 degrees C. It gives a single band on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, corresponding to a mol.wt. of 105,000, and gives a single band on non-denaturing gel electrophoresis at pH8.4. Cross-linking studies at pH8.0 indicate that the subunit structure is tetrameric but that the dimer may also be an important unit of polymerization. Gel filtration results at pH6.7 confirm that the native enzyme is tetrameric with a concentration-dependent dissociation to a dimer. The kinetic behaviour is characterized by (i) relatively small variations in maximum velocity between pH5.5 and 9.0 with a double optimum, (ii) a reversible temperature-dependent inactivation between 30 and 45 degrees C, (iii) inhibition by malate, which is pH-sensitive, and (iv) almost Michaelis-Menten behaviour with phosphoenolpyruvate as the varied ligand but sigmoidal behaviour under suitable conditions with malate as the varied ligand. The findings are related to other studies to the possible role phosphoenolpyruvate carboxylase in controlling a circadian rhythm of CO2 fixation.

Carboxy-Lyases↗
PubMed1976

Molecular and kinetic properties of 15-hydroxyprostaglandin dehydrogenase (PG-15-HDH) from human placenta.

Some molecular properties of PG-15-HDH from human term placenta were investigated. Using a computer-based weighted linear regression analysis, intersecting initial rate patterns were received for the forward reaction with the prostaglandins (PG) E1, E2, and F2alpha, respectively, and NAD as substrates. NADH exerted a linear competitive inhibition with respect to NAD. The 15-ketoprostaglandins (15-keto-PG) E1 and F2alpha showed a linear noncompetitive inhibition with respect to their corresponding PG. The kinetic patterns suggest an ordered Bi Bi mechanism of PG-15-HDH reaction. The results are discussed with respect to their possible biological significance.

Alcohol Oxidoreductases↗
PubMed1976

Phosphofructokinase. III. Correlation of the regulatory kinetic and molecular properties of the rabbit muscle enzyme.

It is shown that the degree of regulatory kinetic behavior of rabbit muscle phosphofructokinase increases at a given pH and lower temperatures, as well as at a given temperature and lower pH values. It is also shown that the regulatory kinetic behavior which appears at lower pH values is inherent in the tetrameric (active) form of the enzyme. We conclude that a portion of the mechanism proposed previously (Bock, P.E., and Frieden, C. (1976) J. Biol. Chem. 251, 5630-5636) to describe the pH and temperature-dependent inactivation or reactivation may also be used to explain the pH and temperature-dependent regulatory kinetic behavior. According to this proposal, two rapidly equilibrating forms of the enzyme, which differ in the degree of protonation of specific residues, differ in their ability to bind substrates. While the protonated form of the enzyme subsequently becomes inactive by isomerization and dissociation, this process is too slow to affect the kinetic results, making direct comparisons between the association-dissociation behavior and regulatory kinetic behavior invalid. The time dependence of the processes of inactivation or reactivation in the presence or absence of ligands and of the appearance of regulatory kinetic behavior is discussed in relation to their possible role in metabolic regulation.

Allosteric Regulation↗
PubMed1979

Immunochemical aspects, molecular and kinetic properties of multiple forms of acetyl-CoA acetyltransferase from rat liver mitochondria.

Acetyl-CoA acetyltransferase (EC 2.3.1.9) from rat liver mitochondria, which catalyzes the first step in the biosynthesis of ketone bodies, exists in two forms, designated transferase A and transferase B. Both transferases showed immunochemical cross-reactivity, but are immunologically unrelated to cytosolic acetyl-CoA acetyltransferase activity and the mitochondrial acetyl-CoA acyltransferase from rat liver. The transferases A and B were estimated to have molecular weights of 151 000 in the absence and 40 000 in the presence of sodium dodecyl sulfate. They differ with respect to charge states and multiplicity of forms as indicated by isoelectric focusing. Transferase A appeared in two forms with isoelectric points of 8.4 and 9.1, whereas transferase B represents a stable protein state with an isoelectric point of 9.0. Kinetic analysis of the reactions leading to acetoacetyl-CoA synthesis revealed saturation curves with multiple intermediary plateaus, indicating a complex kinetic behaviour. The data presented are interpreted as representing a microheterogeneity of forms of the mitochondrial acetyl-CoA acetyltransferase. The kinetic properties exhibited suggest a role for this microheterogeneity in the regulation of ketogenesis.

Acetyl-CoA C-Acetyltransferase↗
PubMedDate not supplied

[Kinetics of reactions in polyenzyme systems. III. Electron transport processes].

Kinetic relationships of electron transport processes in biological systems have been analysed. Formal-kinetic description and discrimination of the two main models of electron transport processes in systems of homogeneously distributed carriers and in systems of structurally bound carriers is presented including steady-state and non-steady-state reaction kinetics. Methods of determination of limit-stage rate constant and rate constants for all elementary steps of the reaction are given. Dependencies of the degree of electron carriers reduction on donor and acceptor concentrations and the influence of reduction or oxidation of carriers on the kinetic properties of electron transport chain (electron influence factor) in the system of structurally-bound carriers have been analyzed. On the basis of kinetic models a molecular-kinetic interpretation of activation effect of mitochondrial respiratory chain during the process of electron transport is offered.

Cytochromes↗
PubMed1976

The influence of chain size and molecular weight on the kinetic constants for the span glucose to polysaccharide for rabbit muscle glycogen synthase.

The kinetic constants for the series of glucosyl acceptors for homogeneous rabbit muscle glycogen synthase I form free of glycogen were examined. The acceptors included glucose, maltose, G3, G4, G6, two hydrolyzed amyloses, amylodextrin and seven polysaccharides including amylopectin and glycogen. S0.5 and relative Vmax were estimated in each case. From these data a two site model of the enzyme is proposed, composed of a polysaccharide binding site and a separate catalytic site, the latter composed of several subsites.

Amylases↗
PubMed1979

Kinetics of the conformational change of troponin-C induced by magnesium-binding or removal.

The kinetics of the conformation change of troponin-C (TN-C) induced by magnesium-binding or removal were studied in the absence of calcium ion by measuring the fluorescence intensity change of BIPM bound to TN-C by stopped-flow spectrofluorometry. The kinetic process of the conformational change was biphasic. The rate constants of the two phases were determined as a function of free magnesium ion concentration ([Mg]) of the solution. The [Mg]-dependence of the rate constants was explained by a simple molecular kinetic mechanism: (formula: see text) The dissociation constant of magnesium bound to TN-C was also determined to be 1 x 10(-3) M in the kinetic study.

Animals↗
PubMed1976

Four-and five-step kinetic models of lactate dehydrogenase.

A five-step model for the reaction catalyzed by beef heart lactate dehydrogenase (EC 1.1.1.27) reconciles differences observed in the four-step model if pre-steady-state data in the forward direction are compared with similar data in the reverse direction. The relationship between the four-and five-step models indicates what problems can develop when an incomplete model is proposed. Nevertheless, there are advantages to using the less complicated four-step model when comparing the molecular kinetics of enzymes catalyzing the same reaction but obtained from different sources.

Animals↗