Chemical and spectroscopic definition of the peroxide-level intermediate in the multicopper oxidases: Relevance to the catalytic mechanism of dioxygen reduction to water
- Stanford Univ., CA (United States)
Laccase is a multicopper oxidase which contains four coppers, one type 1, one type 2, and a coupled binuclear type 3 pair, the type 2 and type 3 copper centers together forming a trinuclear copper cluster. The reaction of reduced type 1 mercury derivative of laccase (T1HgLc) with dioxygen produces an oxygen intermediate which has now been studied in detail. Isotope ratio mass spectrometry (IRMS) has shown that both oxygen atoms of O{sub 2} are bound in the intermediate. EPR and SQUID magnetic suseptibility studies have shown that the intermediate is diamagnetic. The results combined with X-ray absorption edge data indicate that the intermediate contains a bound peroxide and that the two electrons have derived from the type 3 center which is antiferromagnetically coupled. EXAFS data show that there is no short Cu-oxo bond in the intermediate and that there is a new bridging interaction in the intermediate, with two coppers being separated by 3.4 A, that is not present in the resting enzyme. Circular dichroism (CD) and magnetic circular dichroism (MCD) studies in the ligand field region confirm that the two type 3 coppers are oxidized and antiferromagnetically coupled and that the type 2 copper is reduced. In addition, the charge transfer (CT) absorption spectrum of the intermediate supports a {mu}-1, 1 hydroperoxide description based on a comparison to Cu(II)-peroxo model spectra. 67 refs., 15 figs., 2 tabs.
- OSTI ID:
- 232572
- Journal Information:
- Journal of the American Chemical Society, Vol. 118, Issue 13; Other Information: PBD: 3 Apr 1996
- Country of Publication:
- United States
- Language:
- English
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