~10^8 - 10^9 M^-1×sec^-1
||Valko M et al., Redox- and non-redox-metal-induced formation of free radicals and their role in human disease. Arch Toxicol. 2016 Jan90(1):1-37. doi: 10.1007/s00204-015-1579-5 p.6 left column bottom paragraphPubMed ID26343967
||Liochev SI, Fridovich I (1994) The role of O2·− in the production of HO·: in vitro and in vivo. Free Radic Biol Med 16: 29–33. doi:10.1016/0891-5849(94)90239-9PubMed ID8299992
||P.6 left column bottom paragraph: "The release of iron mediated by superoxide radical anion has been demonstrated for the enzymes containing [4Fe–4S] clusters, which contain two ferrous and two ferric ions. Superoxide oxidizes one ferrous ion into a ferric ion according to the reaction (primary source)
[2Fe(II)2Fe(III)−4S]2++O⋅−2+2H+→[Fe(II)3Fe(III)−4S]3++H2O2 (eq. 26) For which the rate constant is about 10^8–10^9 1/M/s."