Dissociation constants of protonated methionine species in NaCl media

Virender K. Sharma, Anthony Zinger, Frank J Millero, Concetta De Stefano

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The sulfur-containing amino acid, methionine, has a role in the physiological environment because of its strong interactions with metals. To understand these interactions of metals with methionine, one needs reliable dissociation constants for the protonated methionine species (NH 3 +CH(CH 2CH 2SCH 3)COOH; H 2B +). The values of stoichiometric dissociation constants, pK i*, for protonated methionine species (H 2B +⇔H ++HB, K 1; HB⇔H ++B -, K 2) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H 2O) -1 and temperature (5-45 °C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H +, H 2B +, HB and B - as a function of ionic strength and temperature. The resulting thermodynamic values of K 1 and K 2 were fit to the equations (T/K): ln K 1=69.0013-3496.58/(T/K)-10.9153 ln (T/K); ln K 2=116.4162-10638.02/(T/K)-18.0553 ln (T/K) with standard errors of 0.003 and 0.033, respectively, for ln K 1* and ln K 2*. Pitzer interaction parameters (λ HB-Na and ζ HB-Na-Cl) for the neutral HB were determined from literature data. The Pitzer parameters (β H2BCl 0, β H2BCl 1 and C H2BCl φ) for the interactions of H 2B + with Cl - and Na + with and B 2-NaB 0, β NaB 1 and C NaB φ) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pK i* for the dissociation of methionine in physiological solutions, composed mostly of NaCl over a wide range of temperature and ionic strength.

Original languageEnglish (US)
Pages (from-to)79-87
Number of pages9
JournalBiophysical Chemistry
Volume105
Issue number1
DOIs
StatePublished - Aug 1 2003

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methionine
Methionine
dissociation
Ionic strength
Osmolar Concentration
Temperature
Metals
methylidyne
Sulfur Amino Acids
Activity coefficients
interactions
coefficients
estimates
Thermodynamics
Sulfur
metals
temperature
amino acids
sulfur
Amino Acids

Keywords

  • Dissociation constants
  • Methionine species
  • NaCl
  • Protonated

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Biophysics

Cite this

Dissociation constants of protonated methionine species in NaCl media. / Sharma, Virender K.; Zinger, Anthony; Millero, Frank J; De Stefano, Concetta.

In: Biophysical Chemistry, Vol. 105, No. 1, 01.08.2003, p. 79-87.

Research output: Contribution to journalArticle

Sharma, VK, Zinger, A, Millero, FJ & De Stefano, C 2003, 'Dissociation constants of protonated methionine species in NaCl media', Biophysical Chemistry, vol. 105, no. 1, pp. 79-87. https://doi.org/10.1016/S0301-4622(03)00137-6
Sharma, Virender K. ; Zinger, Anthony ; Millero, Frank J ; De Stefano, Concetta. / Dissociation constants of protonated methionine species in NaCl media. In: Biophysical Chemistry. 2003 ; Vol. 105, No. 1. pp. 79-87.
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AB - The sulfur-containing amino acid, methionine, has a role in the physiological environment because of its strong interactions with metals. To understand these interactions of metals with methionine, one needs reliable dissociation constants for the protonated methionine species (NH 3 +CH(CH 2CH 2SCH 3)COOH; H 2B +). The values of stoichiometric dissociation constants, pK i*, for protonated methionine species (H 2B +⇔H ++HB, K 1; HB⇔H ++B -, K 2) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H 2O) -1 and temperature (5-45 °C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H +, H 2B +, HB and B - as a function of ionic strength and temperature. The resulting thermodynamic values of K 1 and K 2 were fit to the equations (T/K): ln K 1=69.0013-3496.58/(T/K)-10.9153 ln (T/K); ln K 2=116.4162-10638.02/(T/K)-18.0553 ln (T/K) with standard errors of 0.003 and 0.033, respectively, for ln K 1* and ln K 2*. Pitzer interaction parameters (λ HB-Na and ζ HB-Na-Cl) for the neutral HB were determined from literature data. The Pitzer parameters (β H2BCl 0, β H2BCl 1 and C H2BCl φ) for the interactions of H 2B + with Cl - and Na + with and B 2- (β NaB 0, β NaB 1 and C NaB φ) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pK i* for the dissociation of methionine in physiological solutions, composed mostly of NaCl over a wide range of temperature and ionic strength.

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KW - Protonated

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