||Availability of thiol compounds to generate superoxide by reducing molecular oxygen
Nyui, Minako ,
Ueno, Megumi ,
Nakanishi, IkuoKen-ichiro, Matsumoto
The availability of thiol compounds to generate superoxide by reducing molecular oxygen at hyperthermal temperature was investigated. The reaction properties of cysteine (Cys), N-acetyl-L-cysteine (NAC), reduced form glutathione (GSH), and homocysteine (HCS) were compared. A sulfur-containing amino acid, methionine (Met), biological hydrogen-donor, reduced beta-nicotinamide adenine dinucleotide (NADH), and reduced beta-nicotinamide adenine dinucleotide phosphate (NADPH) were also tested for comparison. An oxidative atmosphere, i.e. superoxide generation by the hypoxanthine-xanthine oxidase reaction, hydroxyl radical generation by X-ray irradiation, or direct one-electron oxidation by ferricyanide, was prepared in a reaction mixture containing 0.1 mM TEMPOL and 1 mM of the test compound, and the EPR signal decay profile of TEMPOL was observed. A reaction mixture containing 0.1 mM TEMPOL and 1 mM thiol compound, Cys, NAC, GSH, or HCS was incubated at 44DegreeC, and the EPR signal decay profile of TEMPOL was observed. Thiols can work as H-donors to the oxoammonium cation form and produce the hydroxyl amine form of TEMPOL in an oxidative atmosphere. Thiols can also irreversibly react with the oxoammonium cation. NAD(P)H could work only as an H-donor. Met did not show any reaction with TEMPOL. GSH and Cys can reduce molecular oxygen to form hydroperoxyl radical/superoxide at hyperthermal temperatures, but HCS and NAC cannot reduce molecular oxygen. GSH and Cys may possibly cause reductive stress, whereas NAC is a simple tractable antioxidant.
Oxygen Radicals, Biology and Pathobiology of Oxygen Radicals from Cell Signaling and Detection to Therapy