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. Author manuscript; available in PMC: 2010 Feb 1.
Published in final edited form as: Mol Aspects Med. 2008 Aug 30;30(1-2):1–12. doi: 10.1016/j.mam.2008.08.006

Fig. 2.

Fig. 2

Redox cycling of 1,4-naphthoquinones. A naphthoquinone with two variable groups (R) can be reduced by NADPH (or NADH, which is not shown) enzymatically to the semiquinone radical and then will react with oxygen to generate superoxide and restore the naphthoquinone.