Abstract
In investigations of the emergence of protocells at the origin of life, repeatable and continuous supply of molecules and ions into the closed lipid bilayer membrane (liposome) is one of the fundamental challenges. Demonstrating an abiotic process to accumulate substances into preformed liposomes against the concentration gradient can provide a clue. Here we show that, without proteins, cell-sized liposomes under hydrodynamic environment repeatedly permeate small molecules and ions, including an analogue of adenosine triphosphate, even against the concentration gradient. The mechanism underlying this accumulation of the molecules and ions is shown to involve their unique partitioning at the liposomal membrane under forced external flow in a constrained space. This abiotic mechanism to accumulate substances inside of the liposomal compartment without light could provide an energetically up-hill process for protocells as a critical step toward the contemporary cells.
Highlights
In investigations of the emergence of protocells at the origin of life, repeatable and continuous supply of molecules and ions into the closed lipid bilayer membrane is one of the fundamental challenges
Contemporary living cells implement cooperative reaction network composed of various membrane proteins involving the consumption of chemical energy sources such as adenosine triphosphate (ATP)[11,12] to overcome this low permeability of the phospholipid membrane
We experimentally explored the unequal kinetics of intake and release suggested from the numerical simulation by measuring the time courses of the ratio of GFI of liposomes (GFIlipo) to GFIBG at a cycle of exposure (5 μM uranine/1 mM fructose; 30 min) and following washout (1 mM fructose; 60 min)
Summary
In investigations of the emergence of protocells at the origin of life, repeatable and continuous supply of molecules and ions into the closed lipid bilayer membrane (liposome) is one of the fundamental challenges. For approximately 30% of trapped liposomes, the green fluorescence intensity (GFI) obtained from the EFM image was maintained at 80% or more of the initial value throughout the exchange of the outer solution (n = 3) (Fig. 3a).
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