Tyrosine Hydrogen Bond Properties for the Two Binding Sites of Apoovotransferrin

Abstract

AbstractThe interaction of gallium(III) with the ligands containing phenolic group(s), such as salicylic acid, 8‐hydroxyquinoline, N,N'‐bis(2‐hydroxybenzyl)ethylenediamine‐N,N′‐diacetic acid (HBED), N,N′‐ethylenebis[2‐(o‐hydroxyphenyl)glycine (EHPG), and ovotransferrin, was studied, respectively, by means of fluorescence in 0.01 mol/L Hepes at pH 7.4 and room temperature. Fluorescence intensity showed an increase when gallium(III) was bound to 8‐hydroxyquinoline and HBED. In contrast, it was decreased with the interaction of gallium(III) with salicylic acid and EHPG. At pH 7.4, there was N···HO type intramolecular hydrogen bond in the former, and the latter existed O···HO type intramolecular hydrogen bond. Fluorescence titration of apoovotransferrin with gallium(III) displayed that the fluorescence intensity was decreased at the N‐terminal binding site, while enhanced at the C‐terminal binding site. It can account for the O···HO type intramolecular hydrogen bonds for the phenolic groups of Tyr92 and Tyr191 residues at the N‐terminal binding site. And there are N···HO type intramolecular hydrogen bonds for Tyr431 and Tyr524 residues at the C‐terminal binding site. In addition, under the same conditions, the conditional binding constant of gallium(III) with EHPG or HBED determined by fluorescence method is lg KGa‐EHPG=19.18 or lg KGa‐HBED=19.08.