 Metabolic network

A metabolic network is a connected system of chemical reactions that transform the metabolites of a biological cell or organism. One reaction's product can be another reaction's substrate, so the activity of one enzyme cannot by itself determine flow through the whole system.

A minimal example has input $u$ into metabolite $A$, conversion $A\to B$ at rate $v$, and removal of $B$ at rate $w$:At a steady state, $u=v=w$. Doubling the maximum capacity of the middle enzyme does not double throughput if the input remains fixed. In a larger metabolic network, the same bookkeeping is expressed as $\dot{\mathbf{x}}=S\mathbf{v}$, with stoichiometric matrix $S$ and metabolic flux vector $\mathbf{v}$.

A genome-scale reconstruction for Escherichia coli combined annotated genes, biochemical literature and strain information to specify possible reactions. The network constrains which conversions are possible; predicting actual rates still needs environmental constraints and modelling assumptions.^[ref]