The Metabolic Wave

Trigger waves — self-propagating fronts of biochemical activity — coordinate large-scale cellular events like mitotic entry and stress responses. They travel faster than diffusion alone would carry a signal, converting an inactive region to active as they pass. The speed and even the direction of these waves depend on the kinetic parameters of the phosphorylation-dephosphorylation cycles that drive them.

Using a thermodynamically consistent reaction-diffusion framework, the intracellular energetic state — ATP concentration and phosphorylation free energy — is shown to be a control variable for trigger-wave behavior. The nonequilibrium parameter γ = [ATP]/(K_eq[ADP][P_i]) modulates wave speed, can reverse propagation direction, reshapes the parameter regimes that support wave existence, and controls the critical nucleus size — the minimum excited region needed for a wave to sustain itself rather than collapse.

The through-claim: the cell's metabolic state is not just the fuel supply for signaling — it is itself a signal. ATP levels are usually treated as a background condition: the energy source that powers the phosphorylation machinery. But if ATP concentration controls wave speed and direction, then fluctuations in metabolic state directly reshape the spatial dynamics of cellular decision-making. The same phosphorylation cascade in a well-fed cell and a stressed cell doesn't just run faster or slower — it can propagate in different directions or fail to propagate at all. Metabolism and signaling are not separate systems where one powers the other. They are coupled, and the coupling runs through the physics of the wave.