Free radical production by activated haem proteins: protective effect of coenzyme Q.

The interaction of hydrogen peroxide with haem proteins leads readily to the formation of myoglobin and/or haemoglobin higher oxidation states (MbIV and/or HbIV), which are capable of promoting the oxidation of cellular costituents and are probably to blame for myocardic tissue damage in ischaemia/reperfusion. This study supports the evidence that the reduced form of Coenzyme Q, like other reducing agents, has an antioxidant activity exerted through the progressive reduction of ferryl forms (MbIV and/or HbIV) back to met and oxy forms (Mb and/or HbIIO2). Furthermore, the strong inactivation afforded by ferryl states of myoglobin on several enzymes, especially creatine kinase (CK), can be prevented by the addition of ubiquinol which protects the enzyme from the oxidative modifications. The ability of ubiquinol to recycle ferryl states of haem proteins provides a novel antioxidant mechanism for Coenzyme Q, besides its direct or indirect antiperoxidative activity, and may represent an important defense mechanism against oxidative tissue injury.