The involvement of oxygen radicals during the autoxidation of adrenalin.
1. In unbuffered alkaline solutions, autoxidizing adrenalin generates superoxide anions: both the scavenging by adrenalin itself, leading to adrenochrome, and the formation of nitrite from hydroxylamine are inhibited by superoxide dismutase. No hydroxyl radical could be detected. 2. The yield of hydrogen peroxide increases with pH in a way similar to that of adrenochrome and nitrite. The dissociated form of adrenalin (pK = 8.5) is proposed as the source of superoxide anions. 3. Superoxide dismutase delays rather than inhibits the reaction. In addition to the diminished formation of adrenochrome due to the scavenging of superoxide anions and re-reduction of the semiquinone by hydrogen peroxide, respectively, adrenochrome is further removed by hydrogen peroxide, with final products absorbing at 310 nm. 4. The diminished inhibitory effect of superoxide dismutase above pH 10 is due to superoxide-independent reactions. This effect is masked by the alkaline conversion of adrenochrome to indole compounds. 5. It is concluded that monitoring the absorption of adrenochrome in alkaline solutions does not produce reliable evidence for superoxide anions.
The involvement of oxygen radicals during the autoxidation of adrenalin. 1. In unbuffered alkaline solutions, autoxidizing adrenalin generates superoxide anions: both the scavenging by adrenalin itself, leading to adrenochrome, and the formation of nitrite from hydroxylamine are inhibited by superoxide dismutase. No hydroxyl radical could be detected. 2. The yield of hydrogen peroxide increases with pH in a way similar to that of adrenochrome and nitrite. The dissociated form of adrenalin (pK = 8.5) is proposed as the source of superoxide anions. 3. Superoxide dismutase delays rather than inhibits the reaction. In addition to the diminished formation of adrenochrome due to the scavenging of superoxide anions and re-reduction of the semiquinone by hydrogen peroxide, respectively, adrenochrome is further removed by hydrogen peroxide, with final products absorbing at 310 nm. 4. The diminished inhibitory effect of superoxide dismutase above pH 10 is due to superoxide-independent reactions. This effect is masked by the alkaline conversion of adrenochrome to indole compounds. 5. It is concluded that monitoring the absorption of adrenochrome in alkaline solutions does not produce reliable evidence for superoxide anions.