Erythrocuprein, also Known as Superoxide Dismutase, Is a Hydroquinone Oxidase, and Imparts Resistance to Mitomycin C

The enzymatic function of superoxide dismutase (SOD) is proposed to be as a ubiquinol oxidase. The SOD activity of this protein is likely a consequence of the necessary dismutation of superoxide (O2˙ˉ), generated as an enzyme-bound intermediate during its normal activity. The relatively low specificity of this enzyme for hydroquinones allowed it to oxidize a wide range of hydroquinone substrates. The general hydroquinone oxidase activity of this enzyme would thus enable it to behave as a mammalian analogue to bacterial mitomycin C resistance protein (MCRA). This would account for its elevated activity in cells expressing resistance against mitomycin C, porfiromycin, and related analogues, since superoxide itself is relatively nontoxic.