Turnover of a Methane Oxidation Tricopper Cluster Catalyst: Implications for the Mechanism of the Particulate Methane Monooxygenase (pMMO)

The (CuCuCuI)-Cu-I-Cu-I tricopper cluster complex is the only known catalyst capable of efficient methane oxidation near room temperature similar to the particulate methane monooxygenase (pMMO). Here, we compare the turnover of the (CuCuCuI)-Cu-I-Cu-I tricopper catalyst with the biochemistry of the functional pMMO. Insights into the turnover of the biomimetic tricopper catalyst are derived from anaerobic electrospray mass spectrometry (ESI-MS) and high-resolution ESI-MS (HR-ESI-MS). We follow activation of the tricopper cluster with O-2/H2O2 by rapid-freeze-quench ESI-MS, high-resolution cold-spray ionization mass spectrometry (HR-CSI-MS) and electron paramagnetic resonance spectroscopy, capturing all the species participating in the activation and deactivation pathways of the turnover cycle. The reactivity of the activated tricopper complex toward alkane oxidation is essentially the same as the biochemistry reported earlier for pMMO from Methylococcus capsulatus (Bath).