Glimpsing the Critical Intermediate in Cytochrome P450 Oxidations

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Science  12 Nov 2010:
Vol. 330, Issue 6006, pp. 924-925
DOI: 10.1126/science.1197881

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Almost all living organisms make use of atmospheric oxygen (O2) for respiration. Another critical role of oxygen is in the partial oxidation of organic compounds, which can remove toxins or create compounds for specialized tasks such as signaling. The enzymes that accomplish this task, the oxygenases, were discovered by Hayaishi in 1955. Among them are the dioxygenases, which insert both of the O atoms into one or more substrates, and the monooxygenases, which incorporate only one of the O atoms into a substrate and reduce the other to water. The cytochrome P450 monooxygenases (P450s) (1), crucial to metabolism, can catalyze a most difficult transformation: the oxidation of aliphatic carbon-hydrogen bonds. The structure of a key intermediate in this reaction, a heme iron bearing a single oxygen atom, has eluded chemists for three decades. On page 933 of this issue, Rittle and Green (2) used Mössbauer and electron paramagnetic resonance spectroscopy, in concert with optical absorption spectroscopy, to characterize this hot oxidant in P450 catalysis as an Fe(IV)-oxo-porphyrin cation radical.