Ionic influences on the phase transition of dipalmitoylphosphatidylserine.

Published

Journal Article

The ionization and phase behavior of 1,2-dipalmitoyl-sn-glycero-3-phosphoserine have been investigated under a variety of condtions by several different methods. As measured by turbidity changes, the temperature of the crystal-liquid crystal phase transition of this lipid is influenced by pH and mono- and divalent cation concentrations. The pH-transition temperature curve is congruent with the curve relating temperature to the degree of ionization of the carboxyl group of the crystalline form. The transition temperature falls from an upper plateau of 72 degrees C at low pH values, where the carboxyl group is fully protonated, to a lower plateau of 55 degrees C at high pH values, where this group is fully ionized. The apparent pK (pH at 50% ionization) of the crystalline form shifts from 6.0 to 4.6 to 3.7 with an increase of NaCl concentration from 10(-3) to 0.1 to l.0 M, respectively. These observations are in accord with a simple theoretical analysis that utilizes diffuse double layer theory and the influence of surface potential on surface concentration of protons. In qualitative terms, an increase in electrolyte concentration reduces the surface potential, the result of which is a diminution of the surface-bulk pH difference and a lowering of the apparent pK. Assuming an area of 50 A2/molecule, the intrinsic pKa (apparent pK corrected for surface pH) of the carboxyl group is 2.7. A 1000-fold change of NaCl concentration produces a very large change in surface potential without influencing the transition temperature of the ionized form of the lipid.

Full Text

Duke Authors

Cited Authors

  • MacDonald, RC; Simon, SA; Baer, E

Published Date

  • February 24, 1976

Published In

Volume / Issue

  • 15 / 4

Start / End Page

  • 885 - 891

PubMed ID

  • 2290

Pubmed Central ID

  • 2290

International Standard Serial Number (ISSN)

  • 0006-2960

Digital Object Identifier (DOI)

  • 10.1021/bi00649a025

Language

  • eng

Conference Location

  • United States