Mitochondrial respiratory chain and thioredoxin reductase regulate intermembrane Cu,Zn-superoxide dismutase activity: implications for mitochondrial energy metabolism and apoptosis

Abstract

IMS (intermembrane space) SOD1 (Cu/Zn-superoxide dismutase) is inactive in isolated intact rat liver mitochondria and is activated following oxidative modification of its critical thiol groups. The present study aimed to identify biochemical pathways implicated in the regulation of IMS SOD1 activity and to assess the impact of its functional state on key mitochondrial events. Exogenous H2O2 (5 microM) activated SOD1 in intact mitochondria. However, neither H2O2 alone nor H2O2 in the presence of mitochondrial peroxiredoxin III activated SOD1, which was purified from mitochondria and subsequently reduced by dithiothreitol to an inactive state. The reduced enzyme was activated following incubation with the superoxide generating system, xanthine and xanthine oxidase. In intact mitochondria, the extent and duration of SOD1 activation was inversely correlated with mitochondrial superoxide production. The presence of TxrR-1 (thioredoxin reductase-1) was demonstrated in the mitochondrial IMS by Western blotting. Inhibitors of TxrR-1, CDNB (1-chloro-2,4-dinitrobenzene) or auranofin, prolonged the duration of H2O2-induced SOD1 activity in intact mitochondria. TxrR-1 inactivated SOD1 purified from mitochondria in an active oxidized state. Activation of IMS SOD1 by exogenous H2O2 delayed CaCl2-induced loss of transmembrane potential, decreased cytochrome c release and markedly prevented superoxide-induced loss of aconitase activity in intact mitochondria respiring at state-3. These findings suggest that H2O2, superoxide and TxrR-1 regulate IMS SOD1 activity reversibly, and that the active enzyme is implicated in protecting vital mitochondrial functions.

Thioredoxin Reductase-2 Is Essential for Keeping Low Levels of H2O2 Emission from Isolated Heart Mitochondria

“…Potential explanations of this result are that (i) TrxR2 inhibition was incomplete in the presence of 100 nM AF, (ii) Trx2 may be reduced by another system independent of TrxR2, or (iii) AF acted on a distinct submitochondrial pool of TrxR2 to increase ROS emission. At this stage, we cannot rule out a potential role of antioxidant systems within the intermembrane space, where TrxR2 (54), TrxR1 (55), and other cytoplasmic antioxidants such as the GSH system (56) and copper/zinc-superoxide dismutase (SOD1) (55) are represented. This certainly warrants future investigation.…”

Thiol switches in mitochondria: operation and physiological relevance

“…In addition, we have identified Grx1 and Grx2 activity in the IMS of yeast cells (Kojer et al, 2014). In humans, Grx1, Sod1, TXNRD1 (Inarrea et al, 2007), GPx1 and GPx4 (Liang et al, 2009) were found to localize to the IMS (Pai et al, 2007). Even more incomplete is our knowledge on the plant IMS.…”

Mechanism-based Proteomic Screening Identifies Targets of Thioredoxin-like Proteins

“…Therefore, a reasonable possibility for the interactions observed in our experiments could be that AIF is a Trx1 reductase in the IMS. Although Trx1 is primarily found in the cytosol, it as well as other primarily cytosolic oxidoreductases, such as glutaredoxin 1 (50) and TR1 (51), and also mitochondrial matrix Trx2 (52), have been found in the IMS. The IMS is known to be a very redox-active compartment and has a system for disulfide bond formation.…”