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Tris buffer causes acyl chain interdigitation in phosphatidylglycerol

Wilkinson, D. A. and Tirrell, D. A. and Turek, A. B. and McIntosh, T. J. (1987) Tris buffer causes acyl chain interdigitation in phosphatidylglycerol. Biochimica et Biophysica Acta - Biomembranes, 905 (2). pp. 447-453. ISSN 0005-2736. doi:10.1016/0005-2736(87)90474-3.

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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° C exists in a lamellar phase in which the hydrocarbon chains are tilted from the perpendicular to the bilayer surface. Around 34°C, there is a small pretransition (ΔH < 1 kcal/mol) followed by the main transition at 40.4°C (ΔH = 8.3 kcal/mol ; ΔV = 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°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°C with ΔH = 9.1 kcal/mol and ΔV = 0.0511 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 ΔV 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.

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Tirrell, D. A.0000-0003-3175-4596
Additional Information:© 1987 Elsevier Science Publishers. Received 1 July 1987. This work was supported by an NSF Presidential Young Investigator Award (D.A.T.), by the Winters Foundation of Pittsburgh, PA, by NSF grant CHE-79-11206, by NIH grant GM 27278, and by NIH grant GM 21128-09. Part of this work was performed in the laboratory of J.F. Nagle whose support and advice are gratefully acknowledged.
Funding AgencyGrant Number
Winters Foundation of Pittsburgh, PAUNSPECIFIED
NIHGM 27278
NIHGM 21128-09
Subject Keywords:Dipalmitoylphosphatidylglycerol; Phase behavior; Interdigitation; X-ray diffraction; Differential scanning calorimetry; Differential scanning dilatometry
Issue or Number:2
Record Number:CaltechAUTHORS:20150122-094455642
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53986
Deposited By: Katherine Johnson
Deposited On:22 Jan 2015 17:59
Last Modified:10 Nov 2021 20:25

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