A study on the interactions between coenzyme Q10 and superoxide anion. Could ubiquinones mimic superoxide dismutase (SOD)?

An electrochemical study was carried out on 1,4-benzoquinone, duroquinone, coenzymes Q(0) and Q(10) in the absence and in the presence of molecular oxygen in aprotic (DMF) and protic (DMF/H2O 95:5 (v/v)) media. Water was added because the investigated reactions are deeply influenced by the presence of protons. Q(0) and Q(10) exhibited a similar electrochemical behaviour. Since Q(0) is more soluble in protic medium than the biologically more important analogue Q(10), it was chosen as a model for a more detailed investigation. Voltammetric studies of Q(0) carried out in aprotic and protic media in the presence of oxygen showed that, besides simple O-2(.-) dismutation, theQ(0) promoted dismutation of O-2(.-) should also be considered. Spectroelectrochemical experiments with the same experimental conditions support the electrochemical results, showing that in the presence of superoxide and in aprotic medium semiquinone Q(0) gives rise to a disproportionation equilibrium, while in the presence of water it tends to be reoxidized to the starting eo by OOH.. EPR measurements are also in agreement with these results.