Hydrogen peroxide induce modifications of human extracellular superoxide dismutase that results in enzyme inhibition

Abstract

Superoxide dismutase (EC-SOD) controls the level of superoxide in the extracellular space by catalyzing the dismutation of superoxide into hydrogen peroxide and molecular oxygen. In addition, the enzyme reacts with hydrogen peroxide in a peroxidase reaction which is known to disrupt enzymatic activity. Here, we show that the peroxidase reaction supports a site-specific bond cleavage. Analyses by peptide mapping and mass spectrometry shows that oxidation of Pro112 supports the cleavage of the Pro112–His113 peptide bond. Substitution of Ala for Pro112 did not inhibit fragmentation, indicating that the oxidative fragmentation at this position is dictated by spatial organization and not by side-chain specificity. The major part of EC-SOD inhibited by the peroxidase reaction was not fragmented but found to encompass oxidations of histidine residues involved in the coordination of copper (His98 and His163). These oxidations are likely to support the dissociation of copper from the active site and thus loss of enzymatic activity. Homologous modifications have also been described for the intracellular isozyme, Cu/Zn-SOD, reflecting the almost identical structures of the active site within these enzymes. We speculate that the inactivation of EC-SOD by peroxidase activity plays a role in regulating SOD activity in vivo, as even low levels of superoxide will allow for the peroxidase reaction to occur.

Reactions of superoxide dismutases with HS−/H2S and superoxide radical anion: An in vitro EPR study

“…encompass the oxidation of His residues involved in the coordination of Cu [29]. Pertinent to this, it has been shown using low-T EPR that H 2 O 2 modifies the structure of catalytic center of CuZnSOD [30].…”

Protective effect of silkworm pupa oil on hydrochloric acid/ethanol‐induced gastric ulcers

“…Previous studies have shown that, after ethanol treatment, due to an increase in free radicals and the reduction of antioxidants, such as SOD, CAT, and GSH‐Px, injury levels of gastric mucosal cells are aggravated, and the degree of superoxide anion generation and cell damage gradually increases with greater alcohol consumption . In response to the accumulation of free radicals, cellular antioxidant enzymes, such as SOD, act as the first line of defense against oxidative damage to cells . Catalase and GSH‐Px have similar effects; these promptly clean up the body of free radicals, so oxidation and the antioxidant status are balanced to protect the body from free radical damage, and the content of antioxidant enzymes directly reflect the amount of free radicals in the body.…”

“…62 In response to the accumulation of free radicals, cellular antioxidant enzymes, such as SOD, act as the first line of defense against oxidative damage to cells. 63 Catalase and GSH-Px have similar effects; these promptly clean up the body of free radicals, so oxidation and the antioxidant status are balanced to protect the body from free radical damage, and the content of antioxidant enzymes directly reflect the amount of free radicals in the body. Copper / Zn-SOD is mainly situated in the cytoplasm, whereas Mn-SOD is located in the mitochondria.…”

Genistein prevents ultraviolet B radiation-induced nitrosative skin injury and promotes cell proliferation

“…In fact, ONOO-is formed by the reaction of NO with O 2 -• which in turn is reduced by SOD, decreasing ONOO -formation [51]. It is also known that H 2 O 2 is a natural inhibitor of SOD [52], and because genistein is able to prevent H 2 O 2 accumulation in the tissue, it will probably leave SOD free to act on O 2 -• decreasing its levels and also inhibiting ONOO-formation.…”