Synergetic effects of Ca2+ and Cu2+ on phase transition in phosphatidylserine membranes |
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Authors: | Kotaro Shirane Shigeko Kuriyama Takayuki Tokimoto |
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Institution: | 1. Biophysics Laboratory, Osaka City University Medical School, Osaka Japan;2. Department of Physiology, Osaka City University Medical School, Osaka Japan |
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Abstract: | In complexes of divalent metals with large exchange rate constant (KH2O) of the coordinated H2O, such as Ca2+ and Cu2+, the cubic structure in the ligand field is usually unstable and conformation changes are easily induced. We observed the molecular motion of phosphatidylserine (PS) in an amphipathic solvent (water / methanol / chloroform) by 1H-NMR and ESR using Ca2+ and / or Cu2+, which has a similar KH2O to that of Ca2+. We found that Ca2+ did not hinder the molecular movements of PS. However, Cu2+ reduced the movements of both headgroups and the double bonds in the fatty acids of PS. By addition of both Ca2+ and Cu2+, phase transition to a soft solid phase in the PS membrane was observed at room temperature. The results indicate that the headgroups are clustered in two-dimensional network with each ligand field displaced from the aqueous phase to the water / oil interface. The structure changes of the polar headgroups after the binding of divalent cations are considered to trigger the phase transition of this acidic phospholipid membrane. |
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Keywords: | Phase transition Phosphatidylserine Phospholipid headgroup Model membrane ESR NMR |
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