Tris buffer causes acyl chain interdigitation in phosphatidylglycerol.

Published

Journal Article

The structure of the gel phase and the properties of the acyl chain disordering transition of dipalmitoyl phosphatidylglycerol (DPPG) have been studied using differential scanning calorimetry, differential scanning dilatometry, and X-ray diffraction. In the presence of small, monovalent cations, DPPG at 22 degrees C exists in a lamellar phase in which the hydrocarbon chains are tilted from the perpendicular to the bilayer surface. Around 34 degrees C, there is a small pretransition (delta H less than 1 kcal/mol) followed by the main transition at 40.4 degrees C (delta H = 8.3 kcal/mol; delta V = 0.0381 ml/g). If DPPG is suspended in Tris-HCl buffer in the absence of other monovalent cations, X-ray diffraction data show that at 22 degrees C, the gel phase consists of interdigitated acyl chains perpendicular to the plane of the bilayer. No pretransition is observed and the main transition occurs at 41.3 degrees C with delta H = 9.1 kcal/mol and delta V = 0.0514 ml/g. If sufficient Na+ or K+ ions are added to the Tris-buffered DPPG, the phase behavior reverts to what is observed in the absence of Tris. Analysis of the energetics of the main transition shows that the increase in van der Waals interaction energy resulting from the larger delta V in Tris can be compensated by the favorable energetics of removing terminal methyl groups from the bilayer surface. The amount of disordering, i.e. formation of gauche rotamers, is likely to be the same in Tris as it is in buffers without amphiphilic cations.

Full Text

Duke Authors

Cited Authors

  • Wilkinson, DA; Tirrell, DA; Turek, AB; McIntosh, TJ

Published Date

  • December 11, 1987

Published In

Volume / Issue

  • 905 / 2

Start / End Page

  • 447 - 453

PubMed ID

  • 3689788

Pubmed Central ID

  • 3689788

International Standard Serial Number (ISSN)

  • 0006-3002

Digital Object Identifier (DOI)

  • 10.1016/0005-2736(87)90474-3

Language

  • eng

Conference Location

  • Netherlands