Members of this protein family are the small subunit (or, in eukaryotes, the N-terminal domain) of xanthine dehydrogenase, an enzyme of purine catabolism via urate. The small subunit contains both an FAD and a 2Fe-2S cofactor. Aldehyde oxidase (retinal oxidase) appears to have arisen as a neofunctionalization among xanthine dehydrogenases in eukaryotes and [Purines, pyrimidines, nucleosides, and nucleotides, Other]
Jiyao W et al.(2023). "The conserved domain database in 2023.",