Uroporphyrinogen III, an intermediate in the biosynthesis of the nickel-containing factor F430 in Methanobacterium thermoautotrophicum.

Factor F430 is a nickel-containing porphinoid present in methanogenic bacteria. The synthesis of this nickel tetrapyrrole from 5-aminolevulinic acid was studied in Methanobacterium thermoautotrophicum. This anaerobic archaebacterium was found to accumulate [14C]uroporphyrinogen III (1.8 mumol/g) when growing on nickel-free medium (less than 50 nmol/l) supplemented with 2 mM 5-amino-[14C]levulinic acid. The accumulated urophorphyrinogen III was quantitatively converted to factor F430 when the cells were incubated in aminolevulinate-free medium with 5 microM NiCl2. The newly synthesized factor had the same specific radioactivity as the precursor uroporphyrinogen III. These findings indicate that the nickelporphinoid is biosynthetically derived from uroporphyrinogen III. The presence and some properties of the enzymes catalyzing the synthesis of uroporphyrinogen III from 5-aminolevulinic acid in M. thermoautotrophicum are also described.