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Tris buffer causes acyl chain interdigitation in phosphatidylglycerol.
D A Wilkinson1, D A Tirrell, A B Turek
1Department of Medical Physics, Allegheny Singer Research Institute, Pittsburgh, PA 15212.
Biochimica Et Biophysica Acta
|December 11, 1987
Summary
The study reveals how buffer ions affect dipalmitoyl phosphatidylglycerol (DPPG) lipid bilayers. Tris-HCl buffer alters DPPG structure and transitions compared to monovalent cations, impacting acyl chain arrangement and phase behavior.
Area of Science:
- Lipid bilayer structure and phase transitions
- Biophysical chemistry of phospholipids
Background:
- Dipalmitoyl phosphatidylglycerol (DPPG) is a common phospholipid model.
- Understanding lipid phase behavior is crucial for membrane biophysics.
Purpose of the Study:
- To investigate the effect of Tris-HCl buffer on DPPG gel phase structure and acyl chain disordering transitions.
- To compare the phase behavior of DPPG in Tris-HCl buffer versus buffers with monovalent cations.
Main Methods:
- Differential scanning calorimetry (DSC)
- Differential scanning dilatometry (DSD)
- X-ray diffraction
Main Results:
- In monovalent cations, DPPG exhibits a lamellar phase with tilted acyl chains at 22°C, a pretransition near 34°C, and a main transition at 40.4°C.
- In Tris-HCl buffer, DPPG shows interdigitated acyl chains perpendicular to the bilayer at 22°C, no pretransition, and a main transition at 41.3°C.
- Addition of Na+ or K+ ions to Tris-buffered DPPG reverts the phase behavior to that observed in the absence of Tris.
Conclusions:
- Tris-HCl buffer significantly alters DPPG's gel phase structure and transition properties compared to monovalent cations.
- Energetic analysis suggests van der Waals interactions and terminal methyl group removal influence the observed phase behavior.
- The degree of acyl chain disordering (gauche rotamer formation) appears similar in Tris-HCl and buffers without amphiphilic cations.