Introduction. Enzymes function within biochemical pathways, exchanging substrates and products to generate useful metabolites. This metabolic context places constraints on enzyme velocity—the product of catalytic activity and enzyme abundance. For example, the relative velocities of some enzymes must be coordinated to avoid accumulation of deleterious metabolic intermediates1,2,3. In other instances, optimal enzyme abundance is set by a tradeoff between the cost of protein synthesis and th...