Synthetic multi-enzymes complexes (MECs) hold promise to increase metabolic fluxes and reduce undesirable and hard-to-characterize contextual interactions with host systems. A major advantage of MECs in metabolism is referred as metabolic channeling [1] wherein a product is channeled to the subsequent active site in the MECs. Yet this mechanism is not very well characterized. We develop a compartmentalized minimal model of two sequential metabolic reactions. We assume that a “vicinity volume” surrounds each enzyme, where the corresponding binding reaction happens. Reactants are assumed to be well-mixed inside the vicinity and in the bulk solution. We explore the advantages of metabolic channeling by comparing bifunctional enzymes (BIFE) and its two corresponding monofunctional enzymes (MOFE) side-by-side using both theoretical analysis and simulations. The theoretical analyses are based on classic Michaelis-Menton Kinetics, the diffusion-controlled reaction rate and the diffusive reaction rate formulated in [2]. Smoldyn is used for simulations [3]. We find that the level of substrate channeling is determined by a governing dimensionless group a, which is the ratio between the diffusive timescale and the reactive timescale. The steady state level of the reactant in the bulk solution in BIFE system is always lower than the MOFE system and a determines the level of this reduction. The dynamical properties also show important differences. Reaction flux is increased in a short timescale in BIFE system compared to MOFE system, and the level of the increase is again determined by the dimensionless parameter a. This increase in flux vanishes after both systems reach the steady state.
