Rat liver uroporphyrinogen III synthase has similar properties to the enzyme from Euglena gracilis, including absence of a requirement for a reversibly bound cofactor for activity.

Uroporphyrinogen III synthase purified from rat liver is a monomer of Mr 36,000 by gel filtration and 28,000 by SDS/polyacrylamide-gel electrophoresis. The enzyme exists in two interconvertible forms separable on h.p.l.c. Both forms of the enzyme could be renatured with full activity after SDS/polyacrylamide-gel electrophoresis, demonstrating the absence of a reversibly bound cofactor. The enzyme activity could be inhibited by pyridoxal 5'-phosphate in the absence and in the presence of NaBH4, consistent with (an) essential lysine residue(s). The enzyme thus shows great similarity to that from Euglena gracilis.