  Biomolecular condensates help organize the cell cytoplasm and nucleoplasm
into spatial compartments with different chemical compositions. A key feature
of such compositional patterning is the local enrichment of enzymatically
active biomolecules which, after transient binding via molecular interactions,
catalyze reactions among their substrates. Thereby, biomolecular condensates
provide a spatial template for non-uniform concentration profiles of
substrates. In turn, the concentration profiles of substrates, and their
molecular interactions with enzymes, drive enzyme fluxes which can enable novel
non-equilibrium dynamics. To analyze this generic class of systems, with a
current focus on self-propelled droplet motion, we here develop a
self-consistent sharp interface theory. In our theory, we diverge from the
usual bottom-up approach, which involves calculating the dynamics of
concentration profiles based on a given chemical potential gradient. Instead,
reminiscent of control theory, we take the reverse approach by deriving the
chemical potential profile and enzyme fluxes required to maintain a desired
condensate form and dynamics. The chemical potential profile and currents of
enzymes come with a corresponding power dissipation rate, which allows us to
derive a thermodynamic consistency criterion for the passive part of the system
(here, reciprocal enzyme-enzyme interactions). As a first use case of our
theory, we study the role of reciprocal interactions, where the transport of
substrates due to reactions and diffusion is, in part, compensated by
redistribution due to molecular interactions. More generally, our theory
applies to mass-conserved active matter systems with moving phase boundaries.
