The enzyme from the aerobic bacterium Ralstonia sp. U2 donates electrons to both EC 1.14.12.12, naphthalene 1,2-dioxygenase and EC 1.14.13.172, salicylate 5-hydroxylase [1]. The enzyme from Pseudomonas NCIB 9816 is specific for the ferredoxin associated with naphthalene dioxygenase; it contains FAD and a [2Fe-2S] cluster.