Some oxygen-dependent oxidoreductases are flavoproteins that contains a covalently bound FAD group which is attached to a histidine via an 8-α-(N3-histidyl)-riboflavin linkage. These proteins are:

• (R)-6-hydroxynicotine oxidase (EC 1.5.3.6) (6-HDNO) [1], a bacterial enzyme that catalyzes the oxygen-dependent degradation of 6-hydroxynicotine into 6-hydroxypyrid-N-methylosmine.
• Plant reticuline oxidase (EC 1.21.3.3) [2] (berberine-bridge-forming enzyme), an enzyme that catalyzes the oxidation of (S)-reticuline into (S)- scoulerine in the pathway leading to benzophenanthridine alkaloids.
• L-gulonolactone oxidase (EC 1.1.3.8) (l-gulono-γ-lactone oxidase) [3], a mammalian enzyme which catalyzes the oxidation of L-gulono-1,4-lactone to L-xylo-hexulonolactone which spontaneously isomerizes to L-ascorbate.
• D-arabinono-1,4-lactone oxidase (EC 1.1.3.24) (L-galactonolactone oxidase), a yeast enzyme involved in the biosynthesis of D-erythroascorbic acid [4].
• Mitomycin radical oxidase [5], a bacterial protein involved in mitomycin resistance and that probably oxidizes the reduced form of mitomycins.
• Cytokinin oxidase (EC 1.4.3.18), a plant enzyme.
• Rhodococcus fascians fasciation locus protein fas5.

The region around the histidine that binds the FAD group is conserved in these enzymes and can be used as a signature pattern.