Figure 1.

Rationale for the Development of a Mitochondrial H₂O₂ Probe

(A) Structure of mitochondria-targeted boronic acid, MitoB, and its phenol product, MitoP, formed by reaction with HOO^- (the conjugate base of H₂O₂).

(B) MitoB uptake into mitochondria within tissues. MitoB is first taken up into cells driven by the plasma membrane potential (Δψ_p), and then accumulates inside the mitochondrial matrix driven by the mitochondrial membrane potential (Δψ_m), resulting in a several-hundred-fold accumulation, as predicted by the Nernst equation. Within mitochondria, MitoB is converted to MitoP in response to H₂O₂. The reaction with H₂O₂ is further enhanced by the higher pH of the matrix relative to the cytoplasm, thus the rate of MitoB to MitoP conversion is an indicator of the mitochondrial H₂O₂ concentration. To measure the MitoP/MitoB ratio, the tissue is spiked with deuterated ISs, extracted, and then quantified by LC-MS/MS.