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Ti(IV) binds to human serum transferrin more tightly than does Fe(III)
Arthur D Tinoco1, Ann M Valentine
1Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520-8107, USA.
Journal of the American Chemical Society
|August 11, 2005
Summary
Titanium(IV) binds human serum transferrin with higher affinity than iron(III), impacting titanium drug efficacy and serum ion binding. This study quantifies titanium-transferrin interactions, revealing significant binding strength differences.
Area of Science:
- Biochemistry
- Metallomics
- Biophysical Chemistry
Background:
- Human serum transferrin (hST) is a key iron-transporting protein.
- Understanding metal ion interactions with hST is crucial for pharmacology and toxicology.
- Titanium(IV) compounds are used in anticancer drugs, implants, and imaging reagents.
Purpose of the Study:
- To quantify the binding affinity of titanium(IV) to human serum transferrin.
- To compare titanium(IV) binding to transferrin with that of iron(III).
- To elucidate the thermodynamic and entropic contributions to titanium(IV) binding.
Main Methods:
- UV/vis kinetics
- Isothermal titration calorimetry (ITC)
- Study of Ti(IV) citrate complex binding to hST at physiological pH and buffer conditions.
Main Results:
- Titanium(IV) exhibits significantly higher binding affinity to transferrin (log K = 26.8 and 25.7) compared to iron(III) (log K = 22.5 and 21.4).
- Binding affinity correlates with the Lewis acidity of the metal ion.
- Titanium(IV) binds preferentially to one transferrin site over the other, influenced by both enthalpy and entropy.
Conclusions:
- Titanium(IV) interaction with transferrin is stronger than iron(III), challenging previous assumptions for metal ions.
- The findings have implications for titanium-based anticancer drug mechanisms and the behavior of titanium ions in biological systems.
- Transferrin plays a significant role in the biological fate and activity of titanium(IV).
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