Abstract
Proton gradients are essential for biological systems. They not only drive the synthesis of ATP, but initiate molecule degradation and recycling inside lysosomes. However, the high mobility and permeability of protons through membranes make pH gradients very hard to sustain in vitro. Here we report that heat flow across a water-filled chamber forms and sustains stable pH gradients. Charged molecules accumulate by convection and thermophoresis better than uncharged species. In a dissociation reaction, this imbalances the reaction equilibrium and creates a difference in pH. In solutions of amino acids, phosphate, or nucleotides, we achieve pH differences of up to 2 pH units. The same mechanism cycles biomolecules by convection in the created proton gradient. This implements a feedback between biomolecules and a cyclic variation of the pH. The finding provides a mechanism to create a self-sustained proton gradient to drive biochemical reactions.
Highlights
Proton gradients are essential for biological systems
In the process of chemiosmosis, for example, the channeled movement of ions across a membrane drives the phosphorylation of ADP to ATP, life’s most commonly used energy currency[7]. Since ancient microbes, such as the last universal common ancestor (LUCA), are assumed to be chemiosmotic[8], it has been argued toward the significance of proton gradients at the origin of life[9,10,11]
Our experimental and theoretical findings show that heat fluxes across confined solutions form and sustain stable pH gradients
Summary
Proton gradients are essential for biological systems. They drive the synthesis of ATP, but initiate molecule degradation and recycling inside lysosomes. Natural pH gradients would form by laminar mixing of fluids with different pH values, e.g., at the interface between disequilibria at submarine hydrothermal vents and the Hadean ocean[16,17,18] These systems rely on a continuous influx of mass and energy. The heat flow forms a temperature gradient, spanning across sub-millimetersized water-filled compartments This is likely a common setting on early earth, found for example in geothermally heated porous rocks such as hydrothermal vents or cooling volcanic sites[19, 20]. This study extends these characteristics to include the formation of a stable pH gradient by thermally separating dissolved buffer molecules of different charge states This locally shifts the buffer equilibrium, yielding pH differences of up to two units and provides another aspect for a promising long-term microhabitat for the onset of molecular evolution. The comparably fast shuttling of vesicles could trigger proton gradients across protocellular membranes without the need for active proton pumps
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