Phthalate dioxygenase reductase (PDR) is an FMN-dependent reductase that mediates electron transfer from NADH to FMN to an iron sulfur cluster. PDR has an an N-terminal ferrredoxin reductase (FNR)-like NAD(H) binding domain and a C-terminal iron-sulfur [2Fe-2S] cluster domain. Although structurally homologous to FNR, PDR binds FMN rather than FAD in it's FNR-like domain. Electron transfer between pyrimidines and iron-sulfur clusters (Rieske center [2Fe-2S]) or heme groups is mediated by flavins in respiration, photosynthesis, and oxygenase systems. Type I dioxygenase systems, including the hydroxylate phthalate system, have 2 components, a monomeric reductase consisting of a flavin and a 2Fe-2S center and a multimeric oxygenase. In contrast to other Rieske dioxygenases the ferredoxin like domain is C-, not N-terminal.