Redox activation of mitochondrial intermembrane space Cu,Zn-superoxide dismutase

Abstract

The localization of Cu,Zn-superoxide dismutase in the mitochondrial intermembrane space suggests a functional relationship with superoxide anion (O 2•− ) released into this compartment. The present study was aimed at examining the functionality of Cu,Znsuperoxide dismutase and elucidating the molecular basis for its activation in the intermembrane space. Intact rat liver mitochondria neither scavenged nor dismutated externally generated O 2•− , unless the mitochondrial outer membrane was disrupted selectively by digitonin. The activation of the intermembrane space Cu,Zn-superoxide dismutase following the disruption of mitochondrial outer membrane was largely inhibited by bacitracin, an inhibitor of protein disulphide-isomerase. Thiol alkylating agents, such as N-methylmaleimide or iodoacetamide, decreased intermembrane space Cu,Zn-superoxide dismutase activation during, but not after, disruption of the outer membrane. This inhibitory effect was overcome by exposing mitochondria to low micromolar concentrations of H 2 O 2 before disruption of the outer membrane in the presence of the alkylating agents. Moreover, H 2 O 2 treatment alone enabled intact mitochondria to scavenge externally generated O 2•− . These findings suggest that intermembrane space Cu,Zn-superoxide dismutase is inactive in intact mitochondria and that an oxidative modification of its critical thiol groups is necessary for its activation.

Deleterious Role of Superoxide Dismutase in the Mitochondrial Intermembrane Space

“…the presence of iodoacetamide) and was expressed as a percentage of activated enzyme in the absence of iodoacetamide (8).…”

“…The fate of superoxide in this compartment is expected to be determined by SOD1 and cytochrome c, which is present in millimolar concentrations (5,6). Recently, cytosolic SOD1 was demonstrated in the yeast (7) and rat (8) IMS, where it has been suggested to be an important part of the mitochondrial superoxide-scavenging system by detoxification of ROS. Cytochrome c is a heme-containing protein that functions as an electron carrier between complex III and cytochrome oxidase in the respiratory chain.…”

Mutant Cu/Zn-Superoxide Dismutase Induced Mitochondrial Dysfunction in Amyotrophic Lateral Sclerosis

“…In animal models the mitochondrial association of mutant SOD1 is apparent even before the disease onset , indicating a causative link of mitochondrial SOD1 to the initiation of pathology. Even though SOD1 has been suggested to be an important part of the mitochondrial superoxide scavenging system, as previously demonstrated in the yeast (Sturtz et al, 2001) and rat (Iñarrea et al, 2005) mitochondrion IMS, SOD1 activity is kept under redox control in this compartment and undergoes activation upon increased hydroperoxide concentration (Iñarrea et al, 2005). There are 4 cysteines in the human SOD1 molecule, located at 6, 57, 111 and 144 position of the sequence.…”

“…According to the model above, the potentiation of mutant SOD1 toxicity by CCS overexpression can be explained by the CCS-mediated increase in SOD1 mitochondrial import, leading to enhanced SOD1 aggregation. In contrast to the model of CCS-dependent activation of mitochondrial SOD1, a number of recent studies suggest that SOD1 in the IMS of intact mitochondria is mostly inactive and an www.intechopen.com oxidative modification of its critical thiol groups is necessary for the activation (Iñarrea et al, 2005(Iñarrea et al, , 2011Goldsteins et al, 2008). This activation, at least partly, depends on protein disulphide isomerase (PDI) activity (Iñarrea et al, 2005).…”

“…In contrast to the model of CCS-dependent activation of mitochondrial SOD1, a number of recent studies suggest that SOD1 in the IMS of intact mitochondria is mostly inactive and an www.intechopen.com oxidative modification of its critical thiol groups is necessary for the activation (Iñarrea et al, 2005(Iñarrea et al, , 2011Goldsteins et al, 2008). This activation, at least partly, depends on protein disulphide isomerase (PDI) activity (Iñarrea et al, 2005). On the other hand, the toxicity of mutant SOD1 is not correlated with its aggregation potential but with the ability to form active dimeric molecules (Witan et al, 2008).…”