Calcium binding to mixed cardiolipin-phosphatidylcholine bilayers as studied by deuterium nuclear magnetic resonance

Journal Article · Tue Sep 22 04:00:00 EDT 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00393a050· OSTI ID:5400302

Macdonald, P M; Seelig, J

Calcium binding to bilayer membranes containing cardiolipin (CDL) mixed with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated by using phosphorus-31 and deuterium nuclear magnetic resonance (NMR) spectroscopy. The destabilizing effect of Ca/sup 2 +/ on CDL bilayers, including the formation of hexagonal H/sub 11/ and isotropic phases, was eliminated when CDL was mixed with sufficiently large proportion of POPC. Specifically head-group-deuteriated CDL or POPC showed in this mixture /sup 2/H NMR spectra indicating that both lipids remained in a fluid-like bilayer at Ca/sup 2 +/ concentrations up to 1.0 M. Any phase separation of Ca/sup 2/-CDL clusters could be excluded. The residence time of Ca/sup 2 +/ at an individual head group binding site was shorter than 10/sup -6/ s. The deuterium quadrupole splitting, ..delta..v/sub Q/, of POPC deuteriated at the ..cap alpha..-methylene segment of the choline head group was found to linearly related to the number of bound calcium ions, X/sub 2/, for the CDL-POPC (1:9 M/M) mixture. The effective surface charged density, sigma, could be determined from the measured amount of bound Ca/sup 2 +/. Subsequently, the surface potential, psi /sub 0/, and the concentration of free Ca/sup 2 +/ ions at the plane of ion binding were calculated by employing the Gouy-Chapman theory. Various possible models of the equilibrium binding of Ca/sup 2 +/ could then be tested. The Langmuir adsorption isotherm with a Ca/sup 2 +/ binding constant of 15.5 M/sup -1/ gave the best fit to the experimental data. Sodium binding was comparatively weak with a binding constant of 0.75 M/sup -1/. A comparison of Ca/sup 2 +/ binding constants for different membrane lipid compositions revealed that the increase in Ca/sup 2 +/ binding observed in the presence of negatively charged lipids was predominantly an electrostatic effect rather than being due to differences in the intrinsic Ca/sup 2 +/ affinity.

• Research Organization: Univ. of Basel, Switzerland
• OSTI ID: 5400302
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:19; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
ABSORPTION SPECTROSCOPY
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CARDIOLIPIN
COMPUTERIZED SIMULATION
CONFIGURATION INTERACTION
DEUTERIUM COMPOUNDS
ESTERS
HYDROGEN COMPOUNDS
ISOTHERMS
ISOTOPES
LIGHT NUCLEI
LIPIDS
MAGNETIC RESONANCE
MEMBRANES
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PHOSPHOLIPIDS
PHOSPHORUS 31
PHOSPHORUS ISOTOPES
RESONANCE
SIMULATION
SPECTROSCOPY
STABLE ISOTOPES