Improved curve fitting procedures to determine equilibrium binding constants

The Analyst ◽  
2006 ◽  
Vol 131 (10) ◽  
pp. 1145 ◽  
Author(s):  
Frank H. Stootman ◽  
Dianne M. Fisher ◽  
Alison Rodger ◽  
Janice R. Aldrich-Wright
Keyword(s):  
Curve Fitting ◽  
Binding Constants ◽  
Equilibrium Binding ◽  
Fitting Procedures

scholarly journals Functional properties of a sarcoplasmic reticulum Ca2+-ATPase with an altered Ca2+-binding mechanism

1995 ◽  
Vol 309 (2) ◽  
pp. 499-505 ◽  
Author(s):  
F Martinez-Azorin ◽  
F Soler ◽  
J C Gomez-Fernandez ◽  
F Fernandez-Belda
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Equilibrium Constants ◽  
Binding Constants ◽  
Binding Mechanism ◽  
Protein Residues ◽  
Equilibrium Binding ◽  
Positive Cooperativity ◽  
Binding Isotherms ◽  
Fitting Procedures ◽  
Equal Amplitude

Treatment of sarcoplasmic reticulum vesicles with diethylpyrocarbonate in the presence of a large excess of reagent, at pH 6.2 and at room temperature, reveals both a fast- and a slow-reacting population of protein residues. The loss of the Ca(2+)-ATPase activity is mainly associated with the fast-reacting population being partially sensitive to hydroxylamine. There is also an effect on the Ca(2+)-binding mechanism. Shorter derivatization times (5 min) produce a loss of the positive cooperativity of Ca2+ binding. When the treatment was prolonged for 30 min there was an additional decrease in the overall Ca2+ affinity. Curve-fitting procedures applied to the non-cooperative binding isotherms provide the equilibrium constants for the two Ca2+ sites, although they cannot discriminate between interacting and independent site mechanisms. Prestationary kinetics assays show 2 Ca2+:1 ATP ratios, at any extent of Ca2+ saturation, indicating that the Ca2+ sites are not independent. The Ca2+ dissociation profile after derivatization shows a decrease in the dissociation constant for the release of the second Ca2+, which is consistent with interacting sites. Isotopic exchange experiments show fast and slow components of equal amplitude even at subsaturating Ca2+ concentrations, which is incompatible with independent binding sites. The experimental data suggest a modification of the equilibrium binding constants making them more similar, but keeping the interacting character. The structural position of the external (cytoplasmic) and the internal (lumenal) Ca2+ sites remains unaltered in the absence of positive cooperativity.

A Fluorescence Quenching Analysis of the Binding of Fluoroquinolones to Humic Acid

2017 ◽  
Vol 71 (11) ◽  
pp. 2512-2518 ◽  
Author(s):  
Ryan P. Ferrie ◽  
Gregory E. Hewitt ◽  
Bruce D. Anderson
Keyword(s):  
Humic Acid ◽  
Fluorescence Quenching ◽  
Water Solubility ◽  
Binding Constants ◽  
High Water ◽  
Static Quenching ◽  
Temperature Range ◽  
Equilibrium Binding ◽  
Quenching Analysis ◽  
High Water Solubility

Fluorescence quenching was used to investigate the interaction of six fluoroquinolones with humic acid. Static quenching was observed for the binding of ciprofloxacin, enoxacin, fleroxacin, levofloxacin, norfloxacin, and ofloxacin to humic acid. The equilibrium binding constants were found from Stern–Volmer plots of the data. The quenching experiments were repeated over a temperature range of 25–45 ℃ and van’t Hoff plots were generated. From these linear plots, thermodynamic values were calculated for Δ H, Δ G, and Δ S for each of the fluoroquinolones. The equilibrium binding constants were found to be <1 for all the antibiotics studied. The calculated ΔH values were all negative and ranged from −9.5 to −27.6 kJ/mol. The high water solubility of the antibiotics and low ΔH of binding suggests that the antibiotics will be transported easily through the environment. Finally, whether the fluoroquinolones are in a protonated, deprotonated, or partially protonated state is found to correlate to the strength of binding to humic acid.

Comparison of reaction theories for multilevel interference—the 14C + p reactions

1969 ◽  
Vol 47 (24) ◽  
pp. 2763-2777 ◽  
Author(s):  
C. T. Tindle ◽  
E. Vogt
Keyword(s):  
Compound Nucleus ◽  
Cross Sections ◽  
Curve Fitting ◽  
Low Energy ◽  
Analytic Method ◽  
R Matrix ◽  
Strong Interference ◽  
S Matrix ◽  
Fitting Procedures ◽  
Good Agreement

A comparison is made between the R-matrix and S-matrix theories of low-energy compound nucleus resonances for the particular case of two-level interference. The (p,γ) and (p,n) cross sections of 14C for proton energies between 0.7 and 1.5 MeV are analyzed using both theories. The 15N compound nucleus in this region exhibits strong two-level interference. The two theories provide equally good fits to the data, but the parameters describing the compound-nucleus levels are quite different. A general analytic method of relating the two sets of parameters is derived and shown to give good agreement with the results obtained by curve-fitting procedures. Remarks are made concerning the general behavior of the parameters under strong interference conditions and also on the inclusion of many channels into the analysis.

A Comparison of Five Curve-Fitting Procedures in Radioimmunoassay

1986 ◽  
Vol 23 (6) ◽  
pp. 694-698 ◽  
Author(s):  
Jennifer A Nisbet ◽  
J A Owen ◽  
Gail E Ward
Keyword(s):  
Binding Site ◽  
Curve Fitting ◽  
The Other ◽  
Practical Advantage ◽  
Analytical Precision ◽  
Fitting Procedures ◽  
Best Fit ◽  
Single Binding Site ◽  
Better Than

Data obtained from routine analytical radioimmunoassays were processed using five curve-fitting procedures, viz. ‘Amersham’, single binding site, four parameter logistic, a linear logit-log and a polynomial logit-log. The polynomial logit-log procedure gave the best fit, but this was probably due to the inherent flexibility of this curve-fitting process since the analytical precision achieved with it was no better than what was obtained with most of the other procedures. A limited study failed to show that statistical weighting of data before curve fitting had any practical advantage.

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