Abstract
Flavins are very versatile coenzymes, and flavoenzymes catalyze various oxidation-reduction reactions. The selection of a specific catalytic reaction from various functions is accomplished by the interactive network of flavin ring, apoenzyme, and substrate. Therefore, the information about the interaction is essential for elucidation of the reaction mechanism on molecular levels. We investigated the molecular interaction of FAD encountered in the active site of flavoproteins (medium-chain acyl-CoA dehydrogenase (MCAD) and electron-transferring flavoprotein (ETF)) by FTIR spectroscopy using C=O stretching as a probe. The 1645-cm−1 band of FAD shifted to 1630 cm−1 in the MCAD-bound form. The low frequency shift can be explained by hydrogen bonds at C(2)=O of the flavin in the MCAD active site. The band was observed at 1607 cm−1 in the charge-transfer complex of MCAD with 3-thiaoctanoyl-CoA. In the case of ETF, two bands of C(4)=O stretching mode were observed at 1712 and 1686 cm−1, indicating multiple conformations of ETF: one with a strong hydrogen-bond, and the other with a weak hydrogen-bond at C(4)=O. [J Physiol Sci. 2007;57 Suppl:S122]
