| 17875556 |
Nishina Y, Sato K, Setoyama C, Tamaoki H, Miura R, Shiga K: Intramolecular and intermolecular perturbation on electronic state of FAD free in solution and bound to flavoproteins: FTIR spectroscopic study by using the C = O stretching vibrations as probes. J Biochem. 2007 Aug;142(2):265-72.
The intramolecular and intermolecular perturbation on the electronic state of FAD was investigated by FTIR spectroscopy by using the C=O stretching vibrations as probes in D (2) O solution. Natural and artificial FADs, i.e. 8-CN-, 8-Cl-, 8-H-, 8-OCH (3)-, and 8-NH (2)-FAD labelled by 2-(13) C, (18) O=C (2), or 4,10a-(13) C (2) were used for band assignments. The C (2)=O and C (4)=O stretching vibrations of oxidized FAD were shifted systematically by the substitution at the 8-position, i.e. the stronger the electron-donating ability (NH (2) > OCH (3) > CH (3) > H > Cl > CN) of the substituent, the lower the wavenumber region where both the C (2)=O and C (4)=O bands appear. In contrast, the C (4)=O band of anionic reduced FAD scarcely shifted. The 1,645-cm (-1) band containing C (2)=O stretching vibration shifted to 1,630 cm (-1) in the medium-chain acyl-CoA dehydrogenase (MCAD)-bound state, which can be explained by hydrogen bonds at C (2)=O of the flavin ring. The band was observed at 1,607 cm (-1) in the complex of MCAD with 3-thiaoctanoyl-CoA. The 23 cm (-1) shift was explained by the charge-transfer interaction between oxidized flavin and the anionic acyl-CoA. In the case of electron-transferring flavoprotein, two bands associated with the C (4)=O stretching vibration were obtained at 1,712 and 1,686 cm (-1), providing evidence for the multiple conformations of the protein. |
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