Fig. 1

Schematic diagram describing the discrepancy in efficiency between glycolysis and the product-forming pathway and the concept of a metabolic valve. In the general case, the native Flux_Glycolysis exceeds the engineered Capacity_{Product-forming pathway A} (width of pipelines), resulting in the leakage of excess carbon as a by-product. In the opposite case, the Capacity_{Product-forming pathway B} is enough to cover glycolytic flux; therefore, overall production rates are determined by Capacity_Glycolysis. Using a metabolic valve, the glycolytic flux could be tuned down for product A (denoted gage as ‘lower’) or amplified for product B (denoted gage as ‘higher’)