Collect. Czech. Chem. Commun. 1997, 62, 1533-1543

Human Orosomucoid: Dissociation of Tyrosines in the Systems Water-Low Aliphatic Alcohol

Vladimír Karpenkoa, Jana Horálkováa and Milan Kodíčekb

a Department of Physical and Macromolecular Chemistry, Charles University, 128 40 Prague 2, Czech Republic
b Department of Biochemistry and Microbiology, Prague Institute of Chemical Technology, 166 28 Prague 6, Czech Republic


The influence of methanol, ethanol, propan-1-ol, and propan-2-ol on the dissociation of tyrosines of human serum orosomucoid (acid α1-glycoprotein) was studied. The content of alcohols was chosen so that their solutions had the same value of the relative permittivity. Then, the contribution of electrostatic effects was equal in all cases and the observed differences between aqueous and alcoholic solutions reflected other, nonelectrostatic effects in the studied systems. Analysis of the spectrophotometric titration curve revealed three kinds of tyrosine groups (n1, n2, n3), but only the values pK1 and pK2 could be calculated. The observed differences of pK values in aqueous and mixed media are discussed and compared with the structural changes of the orosomucoid molecule.

Keywords: Orosomucoid; Tyrosine dissociation; Alcohols effects; UV-spectroscopy; Isopermittivity conditions.