  We demonstrate that, for a chemical reaction network (CRN) engaged in energy
transduction, its optimal operation from a thermodynamic efficiency standpoint
is contingent upon its working conditions. Analogously to the bicycle gear
system, CRNs have at their disposal several transducing mechanisms
characterized by different yields. We highlight the critical role of the CRN's
elementary flux modes in determining this "gearing" and their impact on
maximizing energy transduction efficiency. Furthermore, we introduce an
enzymatically regulated CRN, engineered to autonomously adjust its "gear",
thereby optimizing its efficiency under different external conditions.
