Inhibition of protein hydroperoxide formation by protein thiols

Abstract

Studies on plasma and cells exposed to hydroxyl and peroxyl radicals have indicated that there are few inhibitors of protein hydroperoxide formation. We have, however, observed a small variable lag period during bovine serum albumin (BSA) oxidation by 2-2' azo-bis-(2-methyl-propionamidine) HCl (AAPH) generated peroxyl radicals, where no protein hydroperoxide was formed. The addition of free cysteine to BSA during AAPH oxidation also produced a lag phase suggesting protein thiols could inhibit protein hydroperoxide formation. The selective reduction of thiols on BSA by beta-mercaptoethanol treatment caused the appearance of a lag period where no protein hydroperoxide was formed during the AAPH mediated oxidation. Increasing free thiol concentration on the BSA increased the lag period. Protein hydroperoxide formation began when the protein thiol concentration dropped below one thiol per BSA molecule. It is unlikely that the lag period is due to gross structural alteration of the reduced protein since blocking the free thiols with N-ethyl maleimide eliminated the lag in protein hydroperoxide formation. Protein thiols were found to be ineffective in inhibiting hydroxyl radical-mediated protein hydroperoxide formation during X-ray radiolysis. Evidence is given for protein thiol oxidation occurring via a free radical mediated chain reaction with both free cysteine and protein bound thiol. The data suggest that reduced protein thiol groups can inhibit protein hydroperoxide formation by scavenging peroxyl radicals.

Oxidative protein damage and antioxidant status in systemic lupus erythematosus

“…Studies on SOD activity in patients with SLE have been inconsistent. Most studies showed that SOD activity was decreased in patients with SLE, 3,15 but other studies showed that it was increased or unchanged 20 . The reported decreased GSH‐Px and catalase activity in serum, plasma, red blood cells and whole blood in patients with SLE 21 are in agreement with our findings, but unaltered catalase activity in plasma and serum has also been reported 4,21 .…”

“…Another significant consequence of free‐radical damage to proteins is the formation of protein hydroperoxides. Protein thiol groups can inhibit protein hydroperoxide formation by scavenging peroxyl radicals 3 . Their measurement in serum provides an indirect reflection of protein oxidation.…”

“…Changes in the activities of the antioxidant enzymes SOD, glutathione peroxidase, catalase and myeloperoxidase have been studied in peripheral blood of patients with SLE 3–15 . However, the results are not very consistent.…”

Bactericidal Antibiotics Induce Toxic Metabolic Perturbations that Lead to Cellular Damage

“…There is also particularly compelling evidence to suggest the participation of vicinal pyrimidine peroxyl radicals in the formation of 8-oxo-dG (Bergeron et al, 2010; Douki et al, 2002). Further, it should be noted that peroxyl radicals are much longer-lived than hydroxyl radicals (Lim et al, 2004; Simandan et al, 1998) and hence 8-oxo-guanine formation elicited by antibiotics could potentially be affected by the presence of antioxidants such as glutathione that react with peroxyl radicals (Platt and Gieseg, 2003). …”

Protein-Lipid Interactions in Different Meat Systems in the Presence of Natural Antioxidants – a Review

“…Generally, it can be assumed that the same reactions, which in protein-lipid food products cause a reduction in the nutritional value or quality due to the modifi cation of the protein fraction, determine the protective effect of peptides on the lipid fraction in the protein-stabilized emulsion model systems and depending on the reference system, these changes are determined as either negative or positive. The antioxidant activity of proteins can be considered at three levels: the properties of proteins as polymers of amphiphilic structure, that is hydrophobic-hydrophilic, which determines, among other aspects, the surfactant activity of these compounds [Viljanen, 2005]; antioxidant activity of individual amino acids [Saito et al, 2003;Platt & Gieseg, 2003;Levine et al, 1996]; and the antioxidant nature of colored macromolecular compounds, which are products of non--enzymatic browning as a result of the interaction of oxidized lipids and proteins [Alaiz et al, 1996. Macromolecular compounds formed as a result of condensation between secondary lipid oxidation products and proteins exhibit moderate antioxidant activity [Chelh et al, 2007].…”