Catalysis-driven active transport across a liquid membrane

Biology masters energy transduction, converting energy between various forms, and employing it to drive its vital processes. Central to this is the ability to use chemical energy for the active transport of substances, pumping ions and molecules across hydrophobic lipid membranes between aqueous (sub)cellular compartments. Biology employs information ratchet mechanisms, where kinetic asymmetry in the fuel-to-waste (i.e., substrate-to-product) conversion results in catalysis-driven active transport. Here, we report an artificial system for catalysis-driven active transport across a liquid hydrophobic membrane, pumping a maleic acid cargo between aqueous compartments. We employ two strategies to differentiate the conditions in either compartment, showing that transmembrane active transport can be driven either by adding fuel to a single compartment, or by differentiating the rates of activation and/or hydrolysis when fuel is present in both compartments. We characterize the nonequilibrium system through complete kinetic analysis. Finally, we quantify the energy transduction achieved by the catalysis-driven active transport, and establish the emergence of positive and negative feedback mechanisms within the system.