scholarly journals Adjustment of K' to varying pH and pMg for the creatine kinase, adenylate kinase and ATP hydrolysis equilibria permitting quantitative bioenergetic assessment.

1995 ◽  
Vol 198 (8) ◽  
pp. 1775-1782 ◽  
Author(s):  
E M Golding ◽  
W E Teague ◽  
G P Dobson
Keyword(s):  
Creatine Kinase ◽  
Gibbs Energy ◽  
Adenylate Kinase ◽  
Atp Hydrolysis ◽  
Equilibrium Constants ◽  
Binding Constants ◽  
Acid Dissociation ◽  
Free Magnesium ◽  
Apparent Equilibrium ◽  
Energy Of Formation

Physiologists and biochemists frequently ignore the importance of adjusting equilibrium constants to the ionic conditions of the cell prior to calculating a number of bioenergetic and kinetic parameters. The present study examines the effect of pH and free magnesium levels (free [Mg2+]) on the apparent equilibrium constants (K') of creatine kinase (ATP: creatine N-phosphotransferase; EC 2.7.3.2), adenylate kinase (ATP:AMP phosphotransferase; EC 2.7.4.3) and adenosinetriphosphatase (ATP phosphohydrolase; EC 3.6.1.3) reactions. We show how K' can be calculated using the equilibrium constant of a specified chemical reaction (Kref) and the appropriate acid-dissociation and Mg(2+)-binding constants at an ionic strength (I) of 0.25 mol l-1 and 38 degrees C. Substituting the experimentally determined intracellular pH and free [Mg2+] into the equation containing a known Kref and two variables, pH and free [Mg2+], enables K' to be calculated at the experimental ionic conditions. Knowledge of K' permits calculation of cytosolic phosphorylation ratio ([ATP]/[ADP][Pi]), cytosolic free [ADP], free [AMP], standard transformed Gibbs energy of formation (delta fG' degrees ATP) and the transformed Gibbs energy of the system (delta fG' ATP) for the biological system. Such information is vital for the quantification of organ and tissue bioenergetics under physiological and pathophysiological conditions.

Adjustment of K' for the creatine kinase, adenylate kinase and ATP hydrolysis equilibria to varying temperature and ionic strength.

1996 ◽  
Vol 199 (2) ◽  
pp. 509-512 ◽  
Author(s):  
W E Teague ◽  
E M Golding ◽  
G P Dobson
Keyword(s):  
Creatine Kinase ◽  
Ionic Strength ◽  
Adenylate Kinase ◽  
Atp Hydrolysis ◽  
Equilibrium Constants ◽  
Experimental Conditions ◽  
Physiological Conditions ◽  
Free Energy Of Formation ◽  
Apparent Equilibrium ◽  
Energy Of Formation

Comparative physiologists and biochemists working with tissues at varying temperatures and ionic strength are required to adjust apparent equilibrium constants (K') of biochemical reactions to the experimental conditions prior to calculating cytosolic bioenergetic parameters (transformed Gibbs free energy of formation, DeltafG' ATP; cytosolic phosphorylation ratio, [ATP]/[ADP][Pi]; [phosphocreatine]: [orthophosphate] ratio [PCr]/[Pi]) and kinetic parameters (free [ADP], [Pi] and [AMP]). The present study shows how to adjust both K' and the equilibrium constants of reference reactions (Kref) of creatine kinase (ATP: creatine N-phosphotransferase; EC 2.7.3.2), adenylate kinase (ATP:AMP phosphotransferase; EC 2.7.4.3) and adenosinetriphosphatase (ATP phosphohydrolase; EC 3.6.1.3) to temperature and ionic strength. This information, together with our previous study showing how to adjust equilibria to varying pH and pMg, is vital for the quantification of organ and tissue bioenergetics of ectotherms and endotherms under physiological conditions.

scholarly journals Magnesium Signaling in Plants

2021 ◽  
Vol 22 (3) ◽  
pp. 1159
Author(s):  
Leszek A. Kleczkowski ◽  
Abir U. Igamberdiev
Keyword(s):  
Equilibrium Constant ◽  
Adenylate Kinase ◽  
Nucleoside Diphosphate Kinase ◽  
Phloem Loading ◽  
Photosynthetic Performance ◽  
Fine Tuning ◽  
Primary Control ◽  
Membrane Bound ◽  
Free Magnesium ◽  
Apparent Equilibrium

Free magnesium (Mg2+) is a signal of the adenylate (ATP+ADP+AMP) status in the cells. It results from the equilibrium of adenylate kinase (AK), which uses Mg-chelated and Mg-free adenylates as substrates in both directions of its reaction. The AK-mediated primary control of intracellular [Mg2+] is finely interwoven with the operation of membrane-bound adenylate- and Mg2+-translocators, which in a given compartment control the supply of free adenylates and Mg2+ for the AK-mediated equilibration. As a result, [Mg2+] itself varies both between and within the compartments, depending on their energetic status and environmental clues. Other key nucleotide-utilizing/producing enzymes (e.g., nucleoside diphosphate kinase) may also be involved in fine-tuning of the intracellular [Mg2+]. Changes in [Mg2+] regulate activities of myriads of Mg-utilizing/requiring enzymes, affecting metabolism under both normal and stress conditions, and impacting photosynthetic performance, respiration, phloem loading and other processes. In compartments controlled by AK equilibrium (cytosol, chloroplasts, mitochondria, nucleus), the intracellular [Mg2+] can be calculated from total adenylate contents, based on the dependence of the apparent equilibrium constant of AK on [Mg2+]. Magnesium signaling, reflecting cellular adenylate status, is likely widespread in all eukaryotic and prokaryotic organisms, due simply to the omnipresent nature of AK and to its involvement in adenylate equilibration.

scholarly journals Structural Fragments Izopolivolframat–Anions and Gibbs Energy of Formation

2015 ◽  
Vol 16 (3) ◽  
pp. 524-527
Author(s):  
G.M. Rozantsev
Keyword(s):  
Mathematical Modeling ◽  
Gibbs Energy ◽  
Standard Gibbs Energy ◽  
Equilibrium Constants ◽  
Building Blocks ◽  
Pitzer Method ◽  
Titration Data ◽  
Thermodynamic Probability ◽  
Energy Of Formation ◽  
Concentration Constants

The method of mathematical modeling (program CLINP 2.1, Newton's method) on the basis of the pH-potentiometric titration data allowed to calculate concentration constants of isopolytungstate anions (IPTA) formation at different ionic forces (I = 0,01 ‑ 0,5 M). Thermodynamic constants of IPTA formation were obtained as a result of processing by Pitzer method using the concentration constans. The standard Gibbs energy of isopolytungstate anions formation were calculated. The last ones allowed to estimate the thermodynamic probability of the reactions, that can be used in the synthesis of salts containing these anions. The structure of known isopolytungstates can be built from the combination of such fragments: WO, W2O, W3O, W4O and W5O. The calculation of standard Gibbs energy of these fragments formation allowed to characterize the structure of hexatungstate-anion W6O20(OH)26-, which does not contain three terminal oxygen atoms. Such approach of using Gibbs energy of building blocks was recommended for prediction of equilibrium constants values in the mathematical modeling.

Thermodynamic properties of montechellite

2019 ◽  
Vol 64 (12) ◽  
pp. 1274-1280
Author(s):  
L. P. Ogorodova ◽  
Yu. D. Gritsenko ◽  
M. F. Vigasina ◽  
A. Yu. Bychkov ◽  
D. A. Ksenofontov ◽  
...  
Keyword(s):  
High Temperature ◽  
Gibbs Energy ◽  
Solution Calorimetry ◽  
Thermochemical Study ◽  
Gibbs Energy Of Formation ◽  
Calvet Microcalorimeter ◽  
Magnesium Orthosilicate ◽  
Calcium And Magnesium ◽  
The Enthalpy Of Formation ◽  
Energy Of Formation

A thermochemical study of natural calcium and magnesium orthosilicate ─ monticellite (Ca1.00Mg0.95)[SiO4] (Khabarovsk Territory, Russia) was carried out on the Tian-Calvet microcalorimeter. The enthalpy of formation from the elements fHоel(298.15 K) = -2238.4 4.5 kJ / mol was determined by the method of high-temperature melt solution calorimetry. The enthalpy and Gibbs energy of formation of monticellite of the theoretical composition of CaMg[SiO4] are calculated: fH0el(298.15 K) = -2248.4 4.5 kJ/mol and fG0el(298.15 K) = -2130.5 4.5 kJ/mol.

Polarimetric and nuclear magnetic resonance studies of the complexation of mercury by thiols

1988 ◽  
Vol 66 (12) ◽  
pp. 3184-3189 ◽  
Author(s):  
Mohamed M. Shoukry ◽  
Bruce V. Cheesman ◽  
Dallas L. Rabenstein
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Formation Constant ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
Rotatory Power ◽  
Acid Dissociation ◽  
Optical Rotatory ◽  
Optical Rotatory Power ◽  
Nuclear Magnetic

The complexation of Hg(II) by glutathione has been studied by polarimetry under conditions of excess ligand with the objective of characterizing formation of the 3:1 complex, Hg(glutathione)3. The optical rotatory power of solutions containing glutathione only and of solutions containing glutathione and Hg(II) at ratios of 2:1, 2.5:1, 3:1, and 4:1 was measured as a function of pH. Acid dissociation constants for the ammonium and thiol groups of glutathione and for the two ammonium groups of Hg(glutathione)2 and the formation constant of the 3:1 complex (Hg(glutathione)2 + glutathione [Formula: see text] Hg(glutathione)3) were determined from the pH dependence of the optical rotatory power. The value obtained for the formation constant, Kf = 1.5 × 103, indicates that binding of the third ligand to form Hg(glutathione)3 is much weaker than binding of the first two glutathione ligands. However, calculations indicate that binding is sufficiently strong that a significant fraction of Hg(II) is present as Hg(glutathione)3 under physiological conditions. Equilibrium constants were also determined by polarimetry and by 13C nuclear magnetic resonance for the displacement of one thiolate ligand by another (RSHgSR + R′SH [Formula: see text] RSHgSR′ + RSH; RSHgSR′ + R′SH [Formula: see text] R′SHgSR′ + RSH). The results indicate that, at pH 5.5 and at physiological pH, the relative stability increases in the order Hg(glutathione)2 < Hg(penicillamine)2 < Hg(mercaptoethylamine) 2. However, when competitive protonation of free ligand is accounted for, it is shown that the intrinsic stability of the complexes increases in the order Hg(penicillamine)2 < Hg(mercaptoethylamine)2 < Hg(glutathione)2, which parallels the order of the Brønsted basicity of the thiolate ligands.

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