Uroporphyrinogen-III C-methyltransferase

Uroporphyrinogen-III C-methyltransferase (EC 2.1.1.107), uroporphyrinogen methyltransferase, uroporphyrinogen-III methyltransferase, adenosylmethionine-uroporphyrinogen III methyltransferase, S-adenosyl-L-methionine-dependent uroporphyrinogen III methylase, uroporphyrinogen-III methylase, SirA, CysG, CobA, uroporphyrin-III C-methyltransferase, S-adenosyl-L-methionine:uroporphyrin-III C-methyltransferase) is an enzyme with systematic name S-adenosyl-L-methionine:uroporphyrinogen-III C-methyltransferase.[1][2][3] This enzyme catalyses the following chemical reaction

2 S-adenosyl-L-methionine + uroporphyrinogen III ${\displaystyle \rightleftharpoons }$ 2 S-adenosyl-L-homocysteine + precorrin-2 (overall reaction)

(1a) S-adenosyl-L-methionine + uroporphyrinogen III ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + precorrin-1

(1b) S-adenosyl-L-methionine + precorrin-1 ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + precorrin-2

uroporphyrinogen III substrate of the enzyme

precorrin-2 product of the enzyme

Uroporphyrinogen-III C-methyltransferase catalyses two methylation reactions. The first reaction converts uroporphyrinogen III into precorrin-1. The second converts precorrin-1 into precorrin-2. These reactions are part of the biosynthetic pathway to cobalamin (vitamin B₁₂) in both anaerobic and aerobic bacteria.