Interface of biomolecular condensates modulates redox reactions

Biomolecular condensates mediate diverse cellular processes. The density-transition process of condensate formation results in the selective partitioning of molecules, which defines a distinct chemical environment within the condensates. However, the fundamental features of the chemical environment and the mechanisms by which such an environment can contribute to condensate functions have not been revealed. Here, we report that an electric potential gradient, thereby an electric field, is established at the liquid-liquid interface between the condensate and the bulk environment as a result of the density transition of ions and molecules brought about by phase separation. We find that the interface of condensates can drive spontaneous redox reactions in vitro and in living cells. Our results uncover a fundamental physicochemical property of the interface of condensates and the mechanism by which the interface can modulate biochemical activities.