Theory 06/Metabolic flux/Isotope tracing
Flux Partitioning Is Not Stoichiometry
The claim
How a cell routes carbon is set by the ratio of enzyme capacity to substrate supply at each branch, not by the expression of the enzymes, so transcript abundance mispredicts flux.
01Mechanism
Flux through a branch depends on both the capacity and the supply reaching it; high expression with low supply carries little flux.
02Prediction
Flux should track the capacity-to-supply ratio.
03Refutation
Flux tracking enzyme expression would remove the supply term.
04What makes it checkable
Isotope tracing measures flux directly by following labelled atoms through metabolites, separating capacity from actual flow.
05Why it was not testable before
Expression data described what the cell could do; tracing shows what it is doing.