2.B.37. The Quinol-Triphenylphosphonium Electron Carrier (QTEC) Family
Many mitochondria-targeted antioxidants (MTAs) that comprise a quinol moiety covalently attached through an aliphatic carbon chain to the lipophilic triphenylphosphonium cation are used for evaluating the role of mitochondria in pathological processes involving oxidative stress. MTAs can carry electrons across biological membranes and thereby mediate transmembrane redox processes. Rokitskaya et al. 2016 assessed this by measuring the rate of ferricyanide reduction inside liposomes by external ascorbate. MTAs containing ubiquinone (MitoQ series) or plastoquinone (SkQ series) carry electrons through lipid membranes, with the rate being inversely proportional to the length of the hydrocarbon linker group. This process is stimulated by the hydrophobic anion tetraphenylborate , suggesting that permeation of cationic MTA through the membrane is the rate-limiting step. The rate of MTA-induced electron transfer was insensitive to nigericin, in contrast to electron transfer mediated by neutral quinone derivatives. Thus, MTAs can be utilized to transfer electrons across lipid membranes (Rokitskaya et al. 2016).