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Competitive ion binding to low density lipoproteins: an electron spin resonance study
G Pifat1, L Udovicić, J Brnjas-Kraljević
1Rudjer Bosković Institute, University of Zagreb, Yugoslavia.
Chemistry and Physics of Lipids
|February 1, 1988
Summary
Electron spin resonance (ESR) quantified binding constants for calcium (Ca(II)) and magnesium (Mg(II)) interacting with low-density lipoprotein (LDL). Results reveal distinct binding affinities for these ions at LDL
Area of Science:
- Biochemistry
- Biophysics
- Analytical Chemistry
Background:
- Low-density lipoprotein (LDL) plays a crucial role in cholesterol transport and cardiovascular health.
- Understanding the interaction of divalent metal ions with LDL is essential for elucidating its structure and function.
- Electron spin resonance (ESR) spectroscopy is a sensitive technique for studying paramagnetic species and their binding interactions.
Purpose of the Study:
- To determine the binding constants of calcium (Ca(II)) and magnesium (Mg(II)) ions with LDL.
- To investigate the competition between Ca(II)/Mg(II) and manganese (Mn(II)) for binding sites on the LDL surface.
- To compare the binding affinities of Ca(II) and Mg(II) with LDL to those of Mn(II) and model membranes.
Main Methods:
- Utilized electron spin resonance (ESR) spectroscopy to monitor Mn(II) ion binding to LDL.
- Employed a competition assay where Ca(II) or Mg(II) ions were introduced to displace Mn(II) from LDL binding sites.
- Fitted experimental titration curves to non-linear competition equations to derive binding constants for Ca(II) and Mg(II).
- Calculated intrinsic binding constants by correcting for electrolyte-induced changes in surface potential.
Main Results:
- Identified two classes of binding sites on the LDL surface for divalent metal ions.
- Derived intrinsic binding constants for "strong" sites: Ca(II) (170 ± 85 M⁻¹) and Mg(II) (60 ± 30 M⁻¹), which significantly differ from Mn(II) (760 M⁻¹).
- Determined binding constants for "weak" sites: Mn(II) (18 M⁻¹), Ca(II) (15 M⁻¹), and Mg(II) (10 M⁻¹), comparable to those found with model membranes.
Conclusions:
- Ca(II) and Mg(II) exhibit distinct binding affinities for LDL compared to Mn(II), particularly at strong binding sites.
- The binding behavior of Ca(II) and Mg(II) to weak LDL sites resembles their interaction with lipid bilayers.
- ESR competition assays provide valuable insights into the specific interactions of divalent cations with lipoprotein particles.