Physicochemical Studies on the Binding of Chemicals with Proteins IV. : Hydrogen Ion Equilibria of Lens Proteins

Abstract

In order to find the relationship between electric charge and pH of α- and β-crystallins, the main protein of lens cortical proteins, titration curves of these proteins were calculated. 1) Iso-ionic point of α-crystallin was 5.03 and that of β-crystallin, 5.82. Addition of potassium chloride to the iso-ionic protein solution resulted in increased pH value in both proteins. This was thought to indicate that Cl^- is selectively bounded to both proteins. 2) Titration curves of α- and β-crystallins were obtained for various ionic strength of potassium chloride, using hydrochloric acid and potassium hydroxide. Dissociation of these proteins was found to be affected by other dissociating groups and by chlorine ion. Structural change was found to occur in α-crystallin at around pH 3.7 and in β-crystallin at around pH 3.4.