. "In Saccharomyces cerevisiae, the last two steps are carried out by a single bifunctional enzyme, Met8p." . "This enzyme catalyzes two sequential methylation reactions, the first forming precorrin-1 and the second leading to the formation of precorrin-2." . "It is the first of three steps leading to the formation of siroheme from uroporphyrinogen III." . "The second step involves an NAD(+)-dependent dehydrogenation to form sirohydrochlorin from precorrin-2 (EC 1.3.1.76) and the third step involves the chelation of Fe(2+) to sirohydrochlorin to form siroheme (EC 4.99.1.4)." . "In some bacteria, steps 1-3 are catalyzed by a single multifunctional protein called CysG, whereas in Bacillus megaterium, three separate enzymes carry out each of the steps, with SirA being responsible for the above reaction." . "Also involved in the biosynthesis of cobalamin." . . . "Urogen III methylase" . "SUMT" . "Uroporphyrinogen III methylase" . "Uroporphyrinogen-III C-methyltransferase" . "Uroporphyrin-III C-methyltransferase" . "Uroporphyrinogen-III methyltransferase" . "Uroporphyrinogen-III methylase" . "Adenosylmethionine-uroporphyrinogen III methyltransferase" . "S-adenosyl-L-methionine-dependent uroporphyrinogen III methylase" . "Uroporphyrinogen methyltransferase" . "(1) S-adenosyl-L-methionine + uroporphyrinogen III = S-adenosyl-L-homocysteine + precorrin-1." . "(2) S-adenosyl-L-methionine + precorrin-1 = S-adenosyl-L-homocysteine + precorrin-2." .