Resonance Raman spectra of the FMN of the bovine heart NADH: ubiquinone oxidoreductase, the largest membrane protein in the mitochondrial respiratory system.

The resonance Raman spectra of FMN of the bovine heart NADH: ubiquinone oxidoreductase with the molecular mass of approximately one million dalton were determined by using highly improved enzyme preparation and resonance Raman apparatus. The band positions and the H(2)O/D(2)O exchange effect suggest that the N(3)-H group in the ring III of the isoalloxazine moiety is buried inside the protein to increase the vibrational coupling to the C(2)-N(3)-C(4) stretching mode and that the ring I is exposed to the aqueous phase.