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A study of Ca(2+)-heparin complex-formation by polarimetry
D Grant1, W F Long, C F Moffat
1Department of Molecular and Cell Biology, University of Aberdeen, Marischal College, Scotland, U.K.
The Biochemical Journal
|March 1, 1992
Summary
Calcium ions (Ca2+) may form distinct complexes with heparin, influenced by interaction conditions. The carboxylate group is most important for Ca2+-heparin binding at low ratios, with a 1:1 complex forming at higher ratios.
Area of Science:
- Biochemistry
- Chemical Physics
- Materials Science
Background:
- Heparin is a highly sulfated glycosaminoglycan with significant biological roles.
- Calcium ions (Ca2+) are known to interact with heparin, influencing its structure and function.
- Understanding Ca2+-heparin interactions is crucial for various biomedical applications.
Purpose of the Study:
- To investigate the potential existence of discrete Ca2+-heparin-water complexes.
- To determine the influence of chemical modifications on Ca2+-heparin binding.
- To elucidate the stoichiometry of Ca2+-heparin complex formation under varying conditions.
Main Methods:
- Equilibrium dialysis measurements to assess binding.
- Polarimetric measurements to study structural changes.
- Analysis of chemically modified heparins to probe substituent group importance.
Main Results:
- Inflexions in binding and polarimetric plots suggest discrete Ca2+-heparin-water complexes may form.
- The order of substituent importance for Ca2+ interaction at low ratios is carboxylate > N-sulphonate > N-acetyl > O-sulphate.
- At higher Ca2+/[heparin disaccharide] ratios, a complex with 1:1 stoichiometry forms.
Conclusions:
- The formation and nature of Ca2+-heparin complexes are condition-dependent.
- Specific functional groups on heparin play differential roles in Ca2+ binding.
- A defined stoichiometric complex of Ca2+ and heparin is formed at higher ion concentrations.