Soluble methane monooxygenase (sMMO) facilitates the conversion of methane to methanol at a non-heme Fe IV 2 intermediate MMOH Q , which is formed in the active site of the sMMO hydroxylase component (MMOH) during the catalytic cycle. Other biological systems also employ high-valent Fe IV sites in catalysis; however, MMOH Q is unique as Nature’s only identified Fe IV 2 intermediate. Previous 57 Fe Mössbauer spectroscopic studi...