Major pathways of mitochondrial ROS production and ROS scavenging. The scheme depicts the GSH and Trx systems in the mitochondrial matrix as the major H₂O₂ scavengers. The NADPH/NADP⁺ couple is the main electron donor of the large-capacity GSH (GSH and GSSG) and the Trx (Trx_red and Trx_ox) systems responsible for scavenging H₂O₂ via GPx and Prx enzymes, respectively. GR and TrxR, the two reductases responsible for regenerating the reduced species of both antioxidant defenses, GSH and Trx_red, are shown. The two inhibitors used in this work and their sites of action are highlighted: AF, the TrxR1/2 inhibitor, and DNCB, an alkylating GSH-depleting agent. The respiratory complexes I, II, III, IV, and V (ATP synthase) in the inner mitochondrial membrane (IMM) are also schematized. O₂⁻ can be produced by complexes I and III from the electron transport chain through reverse electron transport (RET) or FET (reverse or forward modes of electron transport), which depends on NADH- or flavin adenine dinucleotide hydrogen–linked substrates, such as G/M or succinate (Succ), donating electrons to complex I or II, respectively. O₂⁻ conversion to H₂O₂ by Mn SOD and the tricarboxylic acid (TCA) cycle are depicted as well. In the scheme of the computational model (see Fig. 4 A), we have split the arrow corresponding to Prx into two processes to account for the cycle of Prx oxidation/reduction as well. These processes are denoted by V_Prx and V_txpx (Eqs. 3 and 5; see Computational model formulation in Materials and methods).