The effect of temperature and ionic strength on the apparent Ca-affinity of EGTA and the analogous Ca-chelators BAPTA and dibromo-BAPTA

Simon M. Harrison, Donald M Bers

Research output: Contribution to journalArticle

171 Citations (Scopus)

Abstract

The apparent calcium association constants (K′Ca) of ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) and 1,2-bis[2-bis(o-amino-5-bromophenoxy)ethane-N,N,N′,N′-tetraacetic acid (dibromo-BAPTA) were measured using the method described by Bers (Am. J. Physiol. 242 (1982) C404-408). The purity of the three ligands determined from the x-intercept of Scatchard plots were 96.3%, 79.0% and 97.3% for EGTA, BAPTA and dibromo-BAPTA, respectively. The impurity of BAPTA was found to be water by drying several samples to constant weight. Increasing temperature from 1 to 36°C led to an increase in K′Ca which was of similar magnitude for the three ligands. Increasing ionic strength from 0.104 to 0.304 M led to a reduction of K′Ca in all cases, though EGTA was affected much less than BAPTA or dibromo-BAPTA. Experimental results were compared with values of K′Ca calculated from the individual association constants of the ligands for calcium and protons which were modified for the experimental conditions using the Debye-Hückel limiting law and the Van't Hoff Isochore to correct for ionic strength and temperature, respectively. The experimental values of K′Ca of EGTA agree well with those in the literature and with the calculated values. Good agreement was also found between the experimental and calculated values of K′Ca for the temperature and ionic strength dependence of BAPTA and dibromo-BAPTA.

Original languageEnglish (US)
Pages (from-to)133-143
Number of pages11
JournalBBA - General Subjects
Volume925
Issue number2
DOIs
StatePublished - Aug 13 1987

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Egtazic Acid
Chelating Agents
Ionic strength
Osmolar Concentration
Temperature
Ethane
Ligands
Acids
Isochores
Association reactions
Calcium
Ethylene Glycol
Ether
Protons
Drying
Impurities
5,5'-dibromo-1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
Water
Weights and Measures

Keywords

  • 1,2-Bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid
  • Affinity constant
  • BAPTA
  • Calcium binding
  • Calcium chelation
  • EGTA
  • Ionic strength

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

Cite this

The effect of temperature and ionic strength on the apparent Ca-affinity of EGTA and the analogous Ca-chelators BAPTA and dibromo-BAPTA. / Harrison, Simon M.; Bers, Donald M.

In: BBA - General Subjects, Vol. 925, No. 2, 13.08.1987, p. 133-143.

Research output: Contribution to journalArticle

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abstract = "The apparent calcium association constants (K′Ca) of ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) and 1,2-bis[2-bis(o-amino-5-bromophenoxy)ethane-N,N,N′,N′-tetraacetic acid (dibromo-BAPTA) were measured using the method described by Bers (Am. J. Physiol. 242 (1982) C404-408). The purity of the three ligands determined from the x-intercept of Scatchard plots were 96.3{\%}, 79.0{\%} and 97.3{\%} for EGTA, BAPTA and dibromo-BAPTA, respectively. The impurity of BAPTA was found to be water by drying several samples to constant weight. Increasing temperature from 1 to 36°C led to an increase in K′Ca which was of similar magnitude for the three ligands. Increasing ionic strength from 0.104 to 0.304 M led to a reduction of K′Ca in all cases, though EGTA was affected much less than BAPTA or dibromo-BAPTA. Experimental results were compared with values of K′Ca calculated from the individual association constants of the ligands for calcium and protons which were modified for the experimental conditions using the Debye-H{\"u}ckel limiting law and the Van't Hoff Isochore to correct for ionic strength and temperature, respectively. The experimental values of K′Ca of EGTA agree well with those in the literature and with the calculated values. Good agreement was also found between the experimental and calculated values of K′Ca for the temperature and ionic strength dependence of BAPTA and dibromo-BAPTA.",
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T1 - The effect of temperature and ionic strength on the apparent Ca-affinity of EGTA and the analogous Ca-chelators BAPTA and dibromo-BAPTA

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N2 - The apparent calcium association constants (K′Ca) of ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) and 1,2-bis[2-bis(o-amino-5-bromophenoxy)ethane-N,N,N′,N′-tetraacetic acid (dibromo-BAPTA) were measured using the method described by Bers (Am. J. Physiol. 242 (1982) C404-408). The purity of the three ligands determined from the x-intercept of Scatchard plots were 96.3%, 79.0% and 97.3% for EGTA, BAPTA and dibromo-BAPTA, respectively. The impurity of BAPTA was found to be water by drying several samples to constant weight. Increasing temperature from 1 to 36°C led to an increase in K′Ca which was of similar magnitude for the three ligands. Increasing ionic strength from 0.104 to 0.304 M led to a reduction of K′Ca in all cases, though EGTA was affected much less than BAPTA or dibromo-BAPTA. Experimental results were compared with values of K′Ca calculated from the individual association constants of the ligands for calcium and protons which were modified for the experimental conditions using the Debye-Hückel limiting law and the Van't Hoff Isochore to correct for ionic strength and temperature, respectively. The experimental values of K′Ca of EGTA agree well with those in the literature and with the calculated values. Good agreement was also found between the experimental and calculated values of K′Ca for the temperature and ionic strength dependence of BAPTA and dibromo-BAPTA.

AB - The apparent calcium association constants (K′Ca) of ethylene glycol bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) and 1,2-bis[2-bis(o-amino-5-bromophenoxy)ethane-N,N,N′,N′-tetraacetic acid (dibromo-BAPTA) were measured using the method described by Bers (Am. J. Physiol. 242 (1982) C404-408). The purity of the three ligands determined from the x-intercept of Scatchard plots were 96.3%, 79.0% and 97.3% for EGTA, BAPTA and dibromo-BAPTA, respectively. The impurity of BAPTA was found to be water by drying several samples to constant weight. Increasing temperature from 1 to 36°C led to an increase in K′Ca which was of similar magnitude for the three ligands. Increasing ionic strength from 0.104 to 0.304 M led to a reduction of K′Ca in all cases, though EGTA was affected much less than BAPTA or dibromo-BAPTA. Experimental results were compared with values of K′Ca calculated from the individual association constants of the ligands for calcium and protons which were modified for the experimental conditions using the Debye-Hückel limiting law and the Van't Hoff Isochore to correct for ionic strength and temperature, respectively. The experimental values of K′Ca of EGTA agree well with those in the literature and with the calculated values. Good agreement was also found between the experimental and calculated values of K′Ca for the temperature and ionic strength dependence of BAPTA and dibromo-BAPTA.

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KW - Ionic strength

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