This domain occurs at the C-terminus of various reductase enzymes, including putidaredoxin reductase, ferredoxin reductase, 3-phenylpropionate/cinnamic acid dioxygenase ferredoxin--NAD(+) reductase component, benzene 1,2-dioxygenase system ferredoxin--NAD(+) reductase subunit, rhodocoxin reductase, biphenyl dioxygenase system ferredoxin--NAD(+) reductase component, rubredoxin-NAD(+) reductase and toluene 1,2-dioxygenase system ferredoxin--NAD(+) reductase component. In putidaredoxin reductase this domain is involved in dimerisation [1]. In the FAD-containing NADH-ferredoxin reductase (BphA4) it is responsible for interaction with the Rieske-type [2Fe-2S] ferredoxin (BphA3) [2].

1: Crystal structure of putidaredoxin reductase from Pseudomonas putida, the final structural component of the cytochrome P450cam monooxygenase. Sevrioukova IF, Li H, Poulos TL; J Mol Biol. 2004;336:889-902. PMID:15095867

2: Molecular mechanism of the redox-dependent interaction between NADH-dependent ferredoxin reductase and Rieske-type [2Fe-2S] ferredoxin. Senda M, Kishigami S, Kimura S, Fukuda M, Ishida T, Senda T; J Mol Biol. 2007;373:382-400. PMID:17850818