  Predicting cellular metabolic states is a central problem in biophysics.
Conventional approaches, however, sensitively depend on the microscopic details
of individual metabolic systems. In this Letter, we derived a universal linear
relationship between the metabolic responses against nutrient conditions and
metabolic inhibition, with the aid of a microeconomic theory. The relationship
holds in arbitrary metabolic systems as long as the law of mass conservation
stands, as supported by extensive numerical calculations. It offers
quantitative predictions without prior knowledge of systems.
