2,2′-Azo-bis-amidinopropane as a radical source for lipid peroxidation and enzyme inactivation studies

Abstract

1. 2,2'-Azo-bis-amidinopropane (ABAP) thermal decomposition produces free radicals that initiate the lipid peroxidation of erythrocyte ghost membranes. 2. Addition of 6-n-propyl-2-thiouracil decreases the rate of the process, both by decreasing consumption of the natural antioxidants of the membranes and by direct interaction with the free radicals involved in the lipid peroxidation. 3. Peroxyl radicals produced in ABAP thermal decomposition inactivate lysozyme, horseradish peroxidase (HRP) and glucose oxidase, in that order. The number of enzyme molecules inactivated per radical introduced into the system increases with enzyme concentration. 4. Competitive studies employing mixtures of enzymes show that the order of reactivity of these enzymes towards the peroxyl radicals is the opposite to that obtained for the rate of enzyme inactivation. It is concluded that inactivation efficiency is determined mainly by the average number of free radicals that must react with an enzyme molecule to produce its inactivation, and that this number is directly related to the molecular weight of the enzyme.

8‐Hydroxy‐1,3,6‐pyrene trisulfonic acid (pyranine) bleaching by 2,2′‐azobis(2‐amidinopropane) derived peroxyl radicals

“…The above results can be interpreted in terms of the following simplified mechanism, followed by protonation of the peroxyanion (ROO − ) formed in reaction (6). In steps (5) and (6), PyOH must comprise both free and AAPH‐complexed pyranine 10. In this scheme should be included radical–radical reactions comprising ROO*, PyO*, and/or R* radicals.…”

“…AAPH was selected as free‐radical source since this species is the most widely employed source of peroxyl radicals in aqueous solution 4. Its pyrolysis in presence of oxygen leads to the formation of peroxyl radicals that can be considered representative of physiologically relevant radicals 10.…”

The Relationship Between Thyroid States, Oxidative Stress and Cellular Damage

“…The biological significance of the oxidative modification of proteins in T 3 -caused liver oxidative stress can be visualized on two levels; 1) loss of protein function and 2) increased protein degradation. Under high rates of ROS and RNS input, the oxidative modification of enzymes can occur with the consequent reduction in enzyme activity (Stadtman, 1990;Lissi et al, 1991). The inactivation of hepatic antioxidant enzymes has been described in several conditions in vivo involving oxidative stress in the tissue, including hyperthyroidism (Lissi et al, 1991), which determines a decrease in the activity of superoxide dismutase and catalase (Fernandez et al, 1988) and in the content of cytochrome P450 (Fernández et al, 1985).…”

“…Under high rates of ROS and RNS input, the oxidative modification of enzymes can occur with the consequent reduction in enzyme activity (Stadtman, 1990;Lissi et al, 1991). The inactivation of hepatic antioxidant enzymes has been described in several conditions in vivo involving oxidative stress in the tissue, including hyperthyroidism (Lissi et al, 1991), which determines a decrease in the activity of superoxide dismutase and catalase (Fernandez et al, 1988) and in the content of cytochrome P450 (Fernández et al, 1985). In agreement with this contention, inactivation of superoxide dismutase by H 2 O 2 (Bray et al, 1974) and of catalase by O 2 .- (Kono & Fridovich, 1982) has been reported in conditions in vitro.…”

Quantitative Treatment of the Kinetics of Free-Radical-Mediated Damage. Protection by Free-Radical Scavengers

“…AAPH ( 2,2'-azobis [2-methylpropanimidamide] dihydrochloride) has been the most frequently employed free-radical source in aqueous solutions [6 ± 9]. This compound produces, in presence of oxygen, peroxyl radicals at a convenient rate (in the order of mm/min) and is very little influenced by the presence of catalysts, such as transition-metal ions [10] [11]. A variety of molecules have been employed as reactive targets [6 ± 10].…”