FAD binding domain. This family consists of various enzymes that use FAD as a co-factor, most of the enzymes are similar to oxygen oxidoreductase. One of the enzymes Vanillyl-alcohol oxidase (VAO) has a solved structure, the alignment includes the FAD binding site, called the PP-loop, between residues 99-110. The FAD molecule is covalently bound in the known structure, however the residue that links to the FAD is not in the alignment. VAO catalyzes the oxidation of a wide variety of substrates, ranging form aromatic amines to 4-alkylphenols. Other members of this family include D-lactate dehydrogenase, this enzyme catalyzes the conversion of D-lactate to pyruvate using FAD as a co-factor; mitomycin radical oxidase, this enzyme oxidises the reduced form of mitomycins and is involved in mitomycin resistance. This family includes MurB an UDP-N-acetylenolpyruvoylglucosamine reductase enzyme EC:1.1.1.158. This enzyme is involved in the biosynthesis of peptidoglycan.

FAD/FMN-containing dehydrogenases [Energy production and conversion]

Berberine and berberine like. This domain is found in the berberine bridge and berberine bridge- like enzymes which are involved in the biosynthesis of numerous isoquinoline alkaloids. They catalyze the transformation of the N-methyl group of (S)-reticuline into the C-8 berberine bridge carbon of (S)-scoulerine.