The mechanism of cumene hydroperoxide-dependent lipid peroxidation: the significance of oxygen uptake.

The addition of limiting amounts of cumene hydroperoxide to rat liver microsomes prepared from phenobarbital-treated rats resulted in the rapid uptake of molecular oxygen, the formation of thiobarbituric acid reactive products, and the loss of hydroperoxide over a similar time course. Maximal activity was observed at pH 7-8. The addition of cumene hydroperoxide to boiled microsomes did not initiate oxygen uptake or produce thiobarbituric acid reactive products. Oxygen uptake was required for the formation of thiobarbituric acid reactive products, but not for the loss of hydroperoxide. The extent of oxygen uptake and thiobarbituric acid reactive product formation was linearly dependent on the concentration of cumene hydroperoxide and independent of the amount of microsomes. For each nanomole of cumene hydroperoxide utilized, 1.5 nmol of oxygen was consumed and 0.11 nmol of thiobarbituric acid reactive products was formed. In addition, a saturable reaction having a high affinity for cumene hydroperoxide was observed that was associated with little or no oxygen uptake and thiobarbituric acid reactive product formation. Butylated hydroxytoluene at substoichiometric concentrations inhibited the extents and initial rates of oxygen uptake and thiobarbituric acid reactive product formation, indicating that cumene hydroperoxide-dependent lipid peroxidation may be an autocatalytic free radical process.