Calcium-induced condensation-reorganization phenomena in multilamellar vesicles of phosphatidic acid. pH potentiometric and 31P-NMR, Raman and ESR spectroscopic studies.
In biological membranes, the anionic characteristics of the polar headgroup of phosphatidic acids are responsible for structural changes induced by Ca2+ in many cellular processes. The very simple headgroup structure of dipalmitoylphosphatidic acid (DPPA) offers particular advantages as a model to study the interactions between Ca2+ and natural phosphatidic acids such as cardiolipin and phosphatidylserine. The effects of calcium ions on DPPA membranes have been studied as a function of temperature by potentiometry and by Raman, ESR and 31P-NMR spectroscopies. The protons in monosodic DPPA liposomes have been considered as a probe to detect pH variations resulting from introduction of Ca2+ inside the membrane. This method has also allowed us to determine the stoichiometry of this reaction: 2 DPPA(H) + Ca2+----Ca(DPPA)2 + 2H+. 31P-NMR spectroscopy has been used to detect reorganization-condensation phenomena in multilamellar vesicles of DPPA under the influence of calcium and temperature. Furthermore, the temperature profiles obtained from Raman spectra for Ca(DPPA)2 membranes provide conclusive evidence that Ca2+ induces major reorganization of the phosphatidic acid component into a highly ordered phase. Quantitative estimates of the degree of motional restriction of spin-labeled soaps embedded inside membranes composed of DPPA with or without Ca2+ have been made using ESR technique. These results are discussed and compared to those found previously for a natural phosphatidic acids such as phosphatidylserine.
Boughriet
A
A
Department of Chemistry, Wayne State University, Detroit, MI.
Ladjadj
M
M
Bicknell-Brown
E
E
D002118:Calcium; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008954:Models, Biological; D010712:Phosphatidic Acids; D010758:Phosphorus; D011199:Potentiometry / Q000379:methods; D013059:Spectrum Analysis, Raman / Q000379:methods
D008081:Liposomes; D010712:Phosphatidic Acids; C031599:dipalmitoylphosphatidic acid; D010758:Phosphorus; D002118:Calcium