When alpha-tocopherol (a-TOH) neutralizes a free radical, such as a lipid hydroperoxyl radical (LOO·), it becomes oxidized itself, forming the alpha-tocopheroxyl radical (a-TO·), which can promote the oxidation of lipoproteins under certain conditions in the test tube (Reaction 1). When the reduced form of coenzyme Q (CoQH2) reacts with a-TO·, a-TOH is regenerated and the semiquinone radical (CoQH·) is formed (Reaction 2). It is possible for CoQH· to react with oxygen (O2) to produce superoxide (O2·-), which is a much less oxidizing radical than LOO· (Reaction 3a). However, CoQH· can also reduce a-TO· back to a-TOH, resulting in the formation of fully oxidized coenzyme Q (CoQ), which does not react with O2 to form O2·- (Reaction 3b).