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Monolayer studies of single-chain polyprenyl phosphates
Katsuhiko Ariga1, Harufumi Yuki, Jun-ichi Kikuchi
1Supermolecules Group, Advanced Materials Laboratory, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan. ariga.katsuhiko@nims.go.jp
Langmuir : the ACS Journal of Surfaces and Colloids
|July 22, 2005
Summary
Primitive membrane lipids like polyprenyl phosphates form stable monolayers at air-water interfaces. Their stability and behavior are influenced by pH and ions, suggesting a pathway for early cell membrane formation.
Area of Science:
- Biophysical chemistry
- Origins of life research
- Membrane biophysics
Background:
- Single-chain polyprenyl phosphates are hypothetical primitive membrane lipids.
- Understanding their behavior is key to understanding early cell formation.
Purpose of the Study:
- Investigate monolayer properties of phytanyl, phytyl, and geranylgeranyl phosphates.
- Determine their behavior at the air-water interface under varying conditions.
- Propose a model for primitive cell membrane formation.
Main Methods:
- Surface pressure-area (pi-A) isotherm measurements at the air-water interface.
- Analysis of pH dependence to determine acid dissociation constants (pKa).
- Investigation of ion effects (Na+, Mg2+, Ca2+, La3+) on monolayer stability.
Main Results:
- Polyprenyl phosphates exhibit distinct pKa values at the air-water interface compared to bilayer states.
- Monolayer stability is significantly affected by pH and the presence of divalent and trivalent metal ions.
- Magnesium and low calcium concentrations stabilize monolayers, while high calcium and lanthanum induce collapse.
Conclusions:
- The pKa shift suggests unique properties of primitive lipids at interfaces.
- Ion interactions play a crucial role in the stability and potential self-assembly of primitive membranes.
- A scenario for monolayer-to-vesicle transformation is proposed, offering insights into early membrane evolution.