Membrane-bound flavin adenine dinucleotide in methanobacterium bryantii

Noncovalently attached flavin was isolated and partially purified from the membrane fraction of Methanobacterium Bryantii. The flavin was identified as FAD by absorption and fluorescence spectroscopy, effects on the spectra of reduction and of protonation, phenol extractability, behavior in thin layer chromatography in two solvent systems, and ability to reconstitute activity of the FAD-specific enzyme D-amino acid oxidase. These singular organisms thus are capable of synthesizing isoalloxazine-type flavins as well as the unique 5-deazaflavin factor F 420. Membrane-bound FAD may thus (in addition to iron-sulfur centers and a nickel species) be involved in energy-coupled methanogenesis.