Hydrogen ion equilibria of alpha-globulin from Sesamum indicum L.

The hydrogen ion equilibrium of the high mol. wt. protein alpha-globulin of sesame seed was investigated in the pH range 2.0-12.0. Analysis of the data gave pKint values of 4.37, 7.47 and 9.60 for carboxyl, imidazole and epsilon-amino groups, resp. The number of residues containing these groups agreed well with values obtained from amino acid analysis. Tyrosyl phenolic groups had a pKint of 9.41 as determined from spectrophotometric titration. The value of the electrostatic interaction parameter, w, varied with pH, and this is discussed in relation to the hydrodynamic properties of the protein.