An Fe_2~ⅣO_2 Diamond Core Structure for the Key Intermediate Q of Methane Monooxygenase

摘要

A new paradigm for oxygen activation is required for enzymes such as methane mono-oxygenase (MMO), for which catalysis depends on a nonheme diiron center instead of the more familiar Fe-porphyrin cofactor. On the basis of precedents from synthetic diiron complexes, a high-valent Fe_2(μ-O)_2 diamond core has been proposed as the key oxidizing species for MMO and other nonheme diiron enzymes such as ribonucleotide reductase and fatty acid desaturase. The presence of a single short Fe-O bond (1.77 angstroms) per Fe atom and an Fe-Fe distance of 2.46 angstroms in MMO reaction intermediate Q, obtained from extended x-ray absorption fine structure and Moessbauer analysis, provides spectroscopic evidence that the diiron center in Q has an Fe_2~ⅣO_2 diamond core.