Spectroscopic characterization of the catalytically competent ferrous site of the resting, activated, and substrate-bound forms of phenylalanine hydroxylase
- Stanford Univ., CA (United States)
- Yale Univ., New Haven, CT (United States)
The geometric structure of the catalytically relevant ferrous active site of phenylalanine hydroxylase (PAH) has been investigated using magnetic circular dichroism (MCD) and X-ray absorption (XAS) spectroscopies. From the excited state ligand field transitions in the MCD spectrum, the temperature and field dependence of these transitions, and the XAS pre-edge shapes and intensities, the resting ferrous site of the `tense` from PAH is six-coordinate distorted octahedral. The low ligand field strength observed in the MCD spectrum results from significant oxygen ligation and longer Fe-O/N bond distances relative to model complexes as determined from an EXAFS analysis. Substrate-induced allosteric activation ({approx}34 kcal/mol) does not alter the structure of the iron site in the `relaxed` form of PAH compared to the substrate-bound `tense` state. Thus, while activation is necessary for the enzyme to achieve complete catalytic competence, it does not appear to affect the geometry of the catalytically relevent six-coordinate ferrous active site and only directly influences the surrounding protein conformation. In contrast, substrate addition results in a geometric and electronic structural change at the iron center which may help orient the substrate for completely coupled hydroxylation. 106 refs., 10 figs., 6 tabs.
- OSTI ID:
- 466979
- Journal Information:
- Journal of the American Chemical Society, Vol. 119, Issue 8; Other Information: PBD: 26 Feb 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
Near-infrared circular dichroism, magnetic circular dichroism, and X-ray absorption spectral comparison of the non-heme ferrous active sites of plant and mammalian 15-lipoxygenases
Spectroscopic definition of the geometric and electronic structure of the non-heme iron active site in iron(II) bleomycin. Correlation with oxygen reactivity