Resonance Raman studies of xanthine oxidase: The reduced enzyme - Product complex with violapterin Article

Hemann, C, Ilich, P, Stockert, AL et al. (2005). Resonance Raman studies of xanthine oxidase: The reduced enzyme - Product complex with violapterin . Journal of Physical Chemistry B, 109(7), 3023-3031. 10.1021/jp046636k

cited authors

  • Hemann, C; Ilich, P; Stockert, AL; Choi, EY; Hille, R

abstract

  • A study of the molecular, electronic, and vibrational characteristics of the molybdenum-containing enzyme complex xanthine oxidase with violapterin has been carried out using density functional theory calculations and resonance Raman spectroscopy. The electronic structure calculations were carried out on a model consisting of the enzyme molybdopterin cofactor [in the four-valent, reduced state; Mo IVCKSH)] covalently linked to violapterin (1H,3H,8H-pteridine-2,4,7-trione in the neutral form) via an oxygen bridge, Mo-O-C7. Full geometry optimizations were performed for all models using the SDD basis set and the three-parameter exchange functional of Becke combined with the Lee, Yang, and Parr correlational functional. Harmonic vibrational frequencies were determined for a variety of isotopes in an attempt to correlate experimentally observed shifts upon 18O-labeling of the Mo-OR bridge to bound product as well as shifts seen upon substitution of solvent-exchangeable protons in samples prepared in D 2O. The theoretical vibrational frequencies compared favorably with experimentally observed vibrational modes in the resonance Raman spectra of the reduced xanthine oxidase-violapterin complex prepared in H 2O and D 2O and with 18O-labeled product. Correlating the isotopic shifts from the calculations with those from the resonance Raman experiments resulted in complete normal mode assignments for all modes observed in the 350-1750 cm -1 range. The present work demonstrates that a model in which the violapterin is coordinated to the molybdenum of the active site in a simple end-on manner via the hydroxyl group introduced by an enzyme accurately predicts the observed resonance Raman spectrum of the complex. Given the numerous modes involving the bridging oxygen, a side-on binding mode can be eliminated. © 2005 American Chemical Society.

authors

publication date

  • February 24, 2005

published in

Digital Object Identifier (DOI)

start page

  • 3023

end page

  • 3031

volume

  • 109

issue

  • 7