Hepatic microsomal metabolism of epinephrine and adrenochrome by superoxide-dependent and -independent pathways

Factors affecting the formation of adrenochrome from epinephrine by the hepatic microsomal fraction in the presence of NADPH have been studied. High oxygen concentrations produced up to a 2-fold increase in the rate of adrenochrome formation, but had no effect upon the rate of superoxide formation by the microsomal fraction, while 10 ⁵M KCN produced a 4-fold increase in the rate of adrenochrome formation from epinephrine and a 50 per cent decrease in the rate of aerobic adrenochrome metabolism. The metabolism of adrenochrome by the microsomal fraction was biphasic. The initial, slower phase of metabolism was oxygen dependent and was inhibited by superoxide dismutase. The second, faster phase occurred only when the dissolved oxygen had been used up and represented the one electron reduction of adrenochrome by NADPH-cytochrome c reductase to form adrenochrome semiquinonc, which then disproportionated to a zwitterionic tautomer of adrenochrome and leucoadrenochrome. The leucoadrenochrome was relatively stable and could be converted back to adrenochrome by reacration of the medium. 5,6-Dihydroxy-N-methylinodole, which has been suggested to be formed from leucoadrenochrome, could not be detected by the techniques employed. In the presence of oxygen, the adrenochrome semiquinone formed by the reduction of adrenochrome was oxidized back to adrenochrome with the formation of superoxide. Superoxide catalyzed the conversion of adrenochrome to adrenolutin.