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siroheme synthase, N-terminal domain This model represents a subfamily of CysG N-terminal region-related sequences. All sequences in the seed alignment for this model are N-terminal regions of known or predicted siroheme synthases. The C-terminal region of each is uroporphyrin-III C-methyltransferase (EC 2.1.1.107), which catalyzes the first step committed to the biosynthesis of either siroheme or cobalamin (vitamin B12) rather than protoheme (heme). The region represented by this model completes the process of oxidation and iron insertion to yield siroheme. Siroheme is a cofactor for nitrite and sulfite reductases, so siroheme synthase is CysG of cysteine biosynthesis in some organisms. [Biosynthesis of cofactors, prosthetic groups, and carriers, Heme, porphyrin, and cobalamin]
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