Calorimetric determination of the micro ionization constants of glutathione

• Published in: Archives of biochemistry and biophysics Vol. 153; no. 1; pp. 55 - 61
• Main Authors: Vander Jagt, David L., Hansen, Lee D., Lewis, Edwin A., Han, Liang-Po B.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.1972
• Subjects: Amines; Calorimetry; Chemical Phenomena; Chemistry, Physical; Glutathione; Mathematics; Protons; Sulfhydryl Compounds; Thermodynamics
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/0003-9861(72)90419-5

The enthalpy changes for ionization of the four acidic protons of glutathione were measured calorimetrically, from both directions, using NaOH and HClO 4 as titrants. For the third and fourth proton ionizations, Δ H = 7.56 and 8.33 kcal/mole, respectively. These are composite values for the overlapping ionizations of the SH and NH 3 + groups of glutathione. The micro-constants for ionization of the SH and NH 3 + groups were determined by resolving the composite enthalpy changes into the fractions prceeding by the sulfhydryl and amino routes. This calculation is based on the assignment of “standard” values to the enthalpy changes for ionization of the SH and NH 3 + groups. The micro-constants calculated are in good agreement with previously reported values obtained by different procedures. The Δ HG∘, Δ HH∘, and Δ HS∘ values measured or calculated for all four ionization steps of glutathione are reported. The data suggest that glutathione has no unusual intramolecular interactions.