title: Kinetics of low pH-induced lamellar to bicontinuous cubic phase transition in dioleoylphosphatidylserine∕monoolein.
abstract: Recently, it has been well recognized that the modulation of electrostatic interactions due to surface charges can induce transitions between lamellar liquid-crystalline (L(α)) and inverse bicontinuous double-diamond cubic (Q(II)(D)) phases in biological lipids. To reveal their kinetic pathway and mechanism, we investigated the low pH-induced L(α) to Q(II)(D) phase transitions in 20%-dioleoylphosphatidylserine (DOPS)/80%-monoolein (MO) using time-resolved small-angle x-ray scattering and a rapid mixing method. At a final pH of 2.6-2.9, the L(α) phase was transformed completely into the hexagonal II (H(II)) phase within 2-10 s after mixing a low pH buffer with a suspension of multilamellar vesicles of 20%-DOPS∕80%-MO (the initial step). Subsequently, the H(II) phase slowly converted into the Q(II)(D) phase and completely disappeared within 15-30 min (the second step). The rate constants of the second step were obtained using the singular value decomposition analysis. On the basis of these data, we discuss the underlying mechanism of the kinetic pathway of the low pH-induced L(α) to Q(II)(D) phase transitions.
authors.affiliation: Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan.
authors.forename: Mahay Md
authors.initials: MM
authors.lastname: Alam
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Oka
authors.forename: Noboru
authors.initials: N
authors.lastname: Ohta
authors.forename: Masahito
authors.initials: M
authors.lastname: Yamazaki
mesh_terms: D005989:Glycerides; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D050866:Liquid Crystals / Q000737:chemistry; D008567:Membranes, Artificial; D044367:Phase Transition; D010718:Phosphatidylserines / Q000737:chemistry*; D053838:Scattering, Small Angle; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D005989:Glycerides; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010718:Phosphatidylserines; C042511:1,2-dioleoylphosphatidylserine; C005953:monoolein