Fig. 3.

Application of Eq. (6) to estimate rate constants between cellular targets and H₂O₂. Plot of the fraction of PTP1B activity observed invitro after 10 min (A) and of the reduced form of KEAP1 observed in HeLa cells after 5 min (B) of incubation with the indicated H₂O₂ concentrations. Experimental data are taken from [33] and [189], respectively for PTP1B and KEAP1. If a simple exponential decay is considered, that is no regeneration of sensor occurs, the slope of these plots is k_{target + H2O2} × t (Eq. (6)) and, therefore, the rate constants between PTP1B and KEAP1 with H₂O₂ are estimated at 22 M⁻¹ s⁻¹ and 20 M⁻¹s⁻¹, respectively. If a gradient between extracellular and intracellular H₂O₂ of 6.8 is considered in HeLa cells [42], the rate constant for H₂O₂ reaction with KEAP1 is estimated at 140 M⁻¹ s⁻¹.