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Zn(2+)-heparin interaction studied by potentiometric titration.
D Grant1, W F Long, F B Williamson
1Department of Molecular and Cell Biology, University of Aberdeen, Marischal College, Scotland, U.K.
The Biochemical Journal
|November 1, 1992
Summary
This study investigated zinc ion (Zn2+) interactions with heparin, revealing a unique complex formation. Unlike other cations, Zn2+ forms a colloid-like complex that can dissolve with increasing ion concentration, indicating non-equilibrium behavior.
Area of Science:
- Biochemistry
- Materials Science
- Physical Chemistry
Background:
- Cation-polyanion interactions are crucial in biological systems.
- Heparin, a highly sulfated polysaccharide, is known to interact with various cations.
- Understanding these interactions is key to developing new biomaterials and drug delivery systems.
Purpose of the Study:
- To investigate the interaction between zinc ions (Zn2+) and heparin.
- To characterize the nature of the complex formed between Zn2+ and heparin.
- To compare Zn2+-heparin interactions with those of other divalent cations.
Main Methods:
- Indirect measurement of cation-polyanion interaction via pH changes upon Zn2+ addition to heparin solutions.
- Analysis of binding using plots analogous to isothermal saturation binding plots.
- Comparison with polarimetric data for Ca2+- and Cu2+-heparin interactions.
Main Results:
- A direct proportionality was observed between the fraction of maximal pH change and the [Zn2+]/[heparin disaccharide] ratio, independent of heparin concentration.
- Zn2+-heparin interaction suggests the formation of a complex in a colloid-like phase, deviating from simple equilibrium thermodynamics.
- The Zn2+-heparin complex appears less stable in NaCl compared to Ca2+-heparin complexes.
- Increased Zn2+ concentration led to a reversal of the initial pH decrease, suggesting complex dissolution.
Conclusions:
- Cation-heparin interactions can form complexes exhibiting non-ideal thermodynamic behavior.
- Zn2+ forms a unique, potentially dissolvable complex with heparin, distinct from other divalent cations studied.
- The findings provide insights into the complexation behavior of heparin with metal ions, relevant for biomedical applications.