are bound symmetrically, suggested by spectroscopic studies. However, the structure is not known. Intermediate P then converts to intermediate Q, which was proposed to contain two antiferromagnetically coupled high-spin FeIV centers. This compound Q with its diamond core is critical to the oxidizing species for MMO. There are two mechanisms suggested for the reaction between compound Q and the alkane: radical and nonradical. The radical mechanism starts with abstraction of the hydrogen atom from the substrate to form QH (the rate determining step), hydroxyl bridged compound Q and the free alkyl radical. The nonradical mechanism implies a concerted pathway, occurring via a four-center transition state and leading to a “hydrido-alkyl-Q” compound. As of 1999, the research suggests that the methane oxidation proceeds via a bound-radical mechanism. It was suggested that the transition state for the radical mechanism involves a torsion motion of the hydroxyl OH ligand before the methyl radical can add to the bridging hydroxyl ligand to form the alcohol. As the radical approaches, the H atom of the alkane leave the coplanar tricoordinate O environment and bends upward to create a tetrahedral tetracoordinate O environment. The final step for this reaction is the elimination of the alcohol and the regeneration of the catalysts. There are a few ways in which this can occur. It could be a stepwise mechanism that starts with the elimination of the alcohol and an intermediate Fe-O-Fe core, and the latter can eliminate the water and regenerate the enzyme through a 2e- reduction. On the other hand, it can start with a 2e- reduction process of bridging the O1 atom to give a water molecule, followed by elimination of the alcohol and regeneration of the enzyme. In addition, it is possible that there is a concerted mechanism whereby the elimination of the methanol occurs spontaneously with 2e- reduction of the bridging O1 center and regeneration of the catalyst. See also Bioinorganic chemistry Oxygenase Shilov system References Further reading External links Enzymes Copper enzymes Metalloproteins Oxidoreductases EC 1.14.13 Integral membrane proteins