INOR 23 |
| Dioxygen activation at the non-heme diiron center of toluene/o-xylene monooxygenase hydroxylase from Pseudomonas sp. proceeds via a diiron(III) intermediate that has been characterized by Mössbauer spectroscopy. This intermediate is kinetically competent to hydroxylate the substrate phenol in the native system or a nearby tryptophan residue in the I100W mutant. Oxidation of tryptophan in the I100W mutant gives rise to a neutral tryptophanyl radical, which is weakly coupled to a mixed-valent diiron(III,IV) species. We propose that this diiron(III) intermediate contains a bound peroxide ion, possibly with an unprecedented geometry or protonation state, by analogy to the mechanism for dioxygen activation in other non-heme diiron systems. No optical absorption bands have yet been observed for this intermediate, and its Mössbauer isomer shift and quadrupole splitting parameters differ from those of the analogous species in related proteins. A mechanism for substrate hydroxylation is presented based on our results. Support for this research was provided by the National Institute of General Medical Sciences. |
|
Bioinorganic Chemistry: Enzymes and Coenzymes
8:30 AM-12:10 PM, Sunday, August 19, 2007 BCEC -- 208, Oral
Division of Inorganic Chemistry |