Fig. 5.

Governing equations of H₂O₂ signaling. The master equation (Eq. 3) includes the dependence on the sustained H₂O₂ signaling concentration [H₂O₂] attained in the vicinity of the redox switch during the signaling process, as well as the rate constants for oxidation (k_target+H2O2) and reduction (k_switchoff) of the redox switch, and the fraction of the redox switch in the reduced form at time 0 (${{\mathrm{Target}}_{\mathrm{rd}}|}_0$). The key features of H₂O₂ signaling are described by two sets of simpler equations deduced from the master Eq. 3 [8], [23]. Eq. 4A is deduced by letting t tend to infinite and represents the steady-state fraction of the redox switch in the oxidized form (Target_ox), which is a measure of the amount of information transmitted from H₂O₂ to the redox target. Calculation of the H₂O₂ signaling concentration causing a certain steady-state value of target oxidation is done with Eq. 4B, which results from an arrangement of Eq. 4A. The second set of equations (Eqs. 5A and 5B) calculates the response time of the redox switch to H₂O₂, giving the time (t_1/2) needed for oxidizing half of the target present initially, i.e., indicating whether transmission of information proceeds rapid enough. Eq. 5A is deduced by replacing ${{\mathrm{Target}}_{\mathrm{rd}}|}_t$ by ${{\mathrm{Target}}_{\mathrm{rd}}|}_0/2$ and t by t_1/2 in Eq. 3 and calculates t_1/2 as a function of H₂O₂ concentration. Eq. 5B is deduced by replacing Eq. 4B in Eq. 5A and calculates t_1/2 as a function of the steady-state fraction of the redox switch in the oxidized form and on the value of k_switchoff.