uroporphyrin-III C-methyltransferase activity obsolete siroheme synthase activity true sirohaem synthase activity OBSOLETE. (Was not defined before being made obsolete). This term was made obsolete because it represents three different molecular functions. siroheme synthase activity molecular_function GO:0009006 siroheme biosynthetic process precorrin-2 dehydrogenase activity sirohydrochlorin ferrochelatase activity