", for example, were able to use glycolytic network extracts, consisting of enzymes from "E. coli" that produced dihydroxyacetone phosphate, to analyze in real-time the metabolite concentrations while altering enzyme levels, with the end result of optimal production of dihydroxyacetone phosphate.Further, Calhoun and Swartz were able to use a glycolytic intermediate to fuel a cell-free system, enabling relatively inexpensive ATP generation compared to reagent usage in phosphoenolpyruvate reactions.