Tyrosine Hydrogen Bond Properties for the Two Binding Sites of Apoovotransferrin

Abstract

The interaction of gallium(III) with the ligands containing phenolic group(s), such as salicylic acid, N, N,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 K Ga-EHPG ＝19.18 or lg K Ga-HBED ＝19.08.

Calorimetric, Spectroscopic, and Model Studies Provide Insight into the Transport of Ti(IV) by Human Serum Transferrin

“…To mimic Ti(IV) coordination and chemistry in this type of binding environment, chelation with HBED was attempted. While HBED is capable of binding a variety of metals, hard metals in particular, HBED 4- binds Fe(III) most strongly (log β = 39.01). − Due to the stability and redox inertness of FeHBED - , HBED has been considered for treatment of iron-overload diseases. − HBED is structurally more flexible than EHPG, and this feature was suggestive that a TiHBED complex could be synthesized in the desired octahedral geometry.…”