Identification and Structure of a Novel Flavin Prosthetic Group Associated with Reduced Nicotinamide Adenine Dinucleotide Dehydrogenase from Peptostreptococcus elsdenii

A novel prosthetic group, which is present in NADH dehydrogenase (EC 1.6.99.3) from Pepfosfrejfococcus etsdenii, has been purified and its physicochemical properties investigated. The chemical structure of this species has been established as the FAD analogue of 7-methyl-8-hydroxyisoalloxazine. The proposed structure is confirmed by: (a) chemical synthesis of 7-methyl-8-hydroxy-isoahoxazine models and comparison of their spectral and physical properties with those of the natural chromophore, and (b) photochemical degradation of the N(lO)-polyhydroxy side chain of the FMN portion of the isolated coenzyme to yield 7-methyl-8-hydroxy-alloxazine. The synthesis of these models is outlined.