title: Non-ideal mixing and fluid-fluid immiscibility in phosphatidic acid-phosphatidylethanolamine mixed bilayers.
abstract: Differential scanning calorimetry (DSC) was used to study the miscibility of phosphatidic acids (PAs) with phosphatidylethanolamines (PEs) as a function of chain length (n = 14, 16) and degree of ionization of PAs at pH 4, pH 7, and pH 12. Phase diagrams were constructed using temperature data for onset and end of the phase transition obtained from the direct simulation of the heat-capacity curves. The phase diagrams were analyzed by simulations of the coexistence curves utilizing a four-parameter regular solution model. For PA-PE mixtures, the non-ideality parameters are a function of composition indicating non-symmetric non-ideal mixing behavior. At pH 7, where the PA component is negatively charged, the systems DMPA:DMPE and DPPA:DPPE have positive non-ideality parameters ρ (1) in both phases, indicating a preferred aggregation of like molecules. In contrast, DMPA:DPPE and DPPA:DMPE mixtures had negative ρ (1) values. Measurements at pH 4 showed that mixed pair formation is favored when PA is protonated. At pH 12 where PA is doubly charged, highly positive ρ (l1) parameters are obtained for the liquid-crystalline phase except for the system DPPA:DPPE (ρ (1) < 0). This indicates clustering of like molecules and possibly domain formation in the liquid-crystalline phase. DPPA:DMPE at pH 12 even shows a miscibility gap in the liquid-crystalline phase. Obviously, despite the presence of doubly charged PA a fluid-fluid immiscibility is induced.
authors: Institute of Chemistry-Physical Chemistry, Martin-Luther-University Halle-Wittenberg, Halle, Saale, Germany.
authors: Patrick
authors: P
authors: Garidel
authors: Christof
authors: C
authors: Johann
authors: Alfred
authors: A
authors: Blume
references: Biochemistry. 1986 Nov 4;25(22):6972-7
references: 3801405
references: Methods Enzymol. 1992;210:521-39
references: 1584050
references: Nat Rev Mol Cell Biol. 2010 Aug;11(8):593-8
references: 20606693
references: Biochim Biophys Acta. 1986 Oct 9;861(2):368-72
references: 3019404
references: Biophys J. 1997 May;72(5):2196-210
references: 9129822
references: Biochemistry. 1979 Apr 17;18(8):1459-68
references: 34426
references: Biochim Biophys Acta. 1977 Nov 14;472(3-4):285-344
references: 143963
references: J Cell Biol. 1974 Jul;62(1):1-19
references: 4600883
references: Biochim Biophys Acta. 1975 Nov 17;413(1):11-23
references: 1191687
references: Biophys J. 1996 Dec;71(6):3215-28
references: 8968592
references: Proc Natl Acad Sci U S A. 1974 Jan;71(1):214-9
references: 4521052
references: Biophys Chem. 1976 Jul;4(4):319-42
references: 8167
references: Biochemistry. 1984 Jul 3;23(14):3227-31
references: 6466639
references: FEBS Lett. 2010 May 3;584(9):1685-93
references: 20036659
references: Prog Biophys Mol Biol. 1975;29(1):3-56
references: 1094490
references: Biochim Biophys Acta. 2008 Nov-Dec;1781(11-12):665-84
references: 18952002
references: Biochim Biophys Acta. 1990 Oct 8;1031(3):311-82
references: 2223819
references: Biochim Biophys Acta. 1979 Jun 2;553(3):476-88
references: 36911
references: Prog Biophys Mol Biol. 1984;43(3):195-257
references: 6087406
references: Biochim Biophys Acta. 1981 Jan 22;640(2):609-18
references: 7213906
references: Biochim Biophys Acta. 2009 Jan;1788(1):72-85
references: 18775410
references: Biochemistry. 1973 Jun 5;12(12):2351-60
references: 4351059
references: Biochim Biophys Acta. 1977 Aug 9;472(2):237-81
references: 329881
references: Biochemistry. 1992 May 19;31(19):4636-42
references: 1316155
references: Biochim Biophys Acta. 1972 Feb 14;265(1):25-60
references: 4552305
references: Science. 2010 Jan 1;327(5961):46-50
references: 20044567
references: Biochim Biophys Acta. 1974 Mar 29;339(3):432-7
references: 4834678
references: Biochim Biophys Acta. 1979 Nov 16;558(1):13-21
references: 40599
references: Biochim Biophys Acta. 1998 Apr 22;1371(1):83-95
references: 9565658
references: Bacteriol Rev. 1975 Sep;39(3):232-56
references: 1100043
references: Biochim Biophys Acta. 2009 Jan;1788(1):47-52
references: 18805392
references: Biochemistry. 1980 Apr 15;19(8):1638-43
references: 6990977
references: Biochemistry. 1975 Feb 25;14(4):847-54
references: 163646
references: Biophys J. 1993 Nov;65(5):1788-94
references: 8298012
references: Biochim Biophys Acta. 1987 Oct 5;906(3):353-404
references: 3307919
references: Eur Biophys J. 2000;28(8):629-38
references: 10663530