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

Journal Article · Tue Mar 10 04:00:00 EST 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00379a005· OSTI ID:6469721

MacDonald, P M; Seelig, J

The binding of calcium to bilayer membranes composed of mixtures, in various proportions, of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) plus 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) was investigated by using atomic absorption spectroscopy and deuterium nuclear magnetic resonance. The number of bound calcium ions, X/sub 2/, was determined in the low calcium concentration range via atomic absorption spectroscopy. Simultaneous measurements of the deuterium magnetic resonance spectra of POPC, specifically deuteriated at the ..cap alpha..-methylene segment of the choline head group, revealed a linear relationship between the quadrupole splitting, ..delta..v/sub Q/, and X/sub 2/ for each particular proportion of POPC-POPG. The amount of bound calcium was then determined at much greater calcium concentration, where the atomic absorption spectroscopy measurements were unreliable, using deuterium magnetic resonance. At low Ca/sup 2 +/ concentrations, the amount of bound Ca/sup 2 +/ increased linearly with increasing proportion of POPG, demonstrating an electrostatic contribution to Ca/sup 2 +/ binding. At high Ca/sup 2 +/ concentrations, the calcium binding isotherms exhibited saturation behavior with a maximum binding capacity of 0.5 Ca/sup 2 +/ and 1.0 Ca/sup 2 +/ per phospholipid for pure POPC and mixtures of POPC-POPG, respectively. Ca/sup 2 +/ ions accumulate near the negatively charged POPG-POPC membrane surface but move freely in a trough of the electrical potential. The effective surface charge density, sigma, could be determined from the measured amount of bound Ca/sup 2 +/. The values of the calcium association constants indicate that the increased binding of calcium with increasing proportion of POPG is predominantly an electrostatic effect, rather than the result of an intrinsically greater affinity of POPG for calcium.

• Research Organization: Biocenter of the Univ. of Basel, Switzerland
• OSTI ID: 6469721
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:5; 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
COMPUTERIZED SIMULATION
CONFIGURATION INTERACTION
DEUTERIUM COMPOUNDS
ESTERS
HYDROGEN COMPOUNDS
ISOTHERMS
LIPIDS
MAGNETIC RESONANCE
MEMBRANES
NUCLEAR MAGNETIC RESONANCE
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PHOSPHOLIPIDS
RESONANCE
SIMULATION
SPECTROSCOPY