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.
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.
Nishina
Yasuzo
Y
Department of Physiology, School of Health Sciences, Kumamoto University, Honjo, Kumamoto 860-8556. nishina@hs.kumamoto-u.ac.jp
Sato
Kyosuke
K
Setoyama
Chiaki
C
Tamaoki
Haruhiko
H
Miura
Retsu
R
Shiga
Kiyoshi
K
D001665:Binding Sites; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry* / Q000378:metabolism; D005420:Flavoproteins / Q000737:chemistry* / Q000378:metabolism; D007553:Isotope Labeling; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
D005420:Flavoproteins; D012996:Solutions; D005182:Flavin-Adenine Dinucleotide