Members of this family are all oxygen-independent coproporphyrinogen-III oxidases (HemN). This enzyme catalyses the oxygen-independent conversion of coproporphyrinogen-III to protoporphyrinogen-IX [1], one of the last steps in haem biosynthesis. The function of this domain is unclear, but comparison to other proteins containing a radical SAM domain (Pfam:PF04055) suggest it may be a substrate binding domain.

1: Terminal steps of haem biosynthesis. Dailey HA; Biochem Soc Trans 2002;30:590-595. PMID:12196143

2: Crystal structure of coproporphyrinogen III oxidase reveals cofactor geometry of Radical SAM enzymes. Layer G, Moser J, Heinz DW, Jahn D, Schubert WD; EMBO J. 2003;22:6214-6224. PMID:14633981