Phosphomethylpyrimidine synthase

Phosphomethylpyrimidine synthase (, thiC (gene)) is an enzyme with systematic name 5-amino-1-(5-phospho- D -ribosyl)imidazole formate-lyase (decarboxylating, 4-amino-2-methyl-5-phosphomethylpyrimidine-forming). This enzyme catalyses the following chemical reaction


 * 5-amino-1-(5-phospho- D -ribosyl)imidazole + S-adenosyl- L -methionine $$\rightleftharpoons$$ 4-amino-2-methyl-5-phosphomethylpyrimidine + 5′-deoxyadenosine + L -methionine + formate + CO

This enzyme binds a 4Fe-4S cluster.
 * Pyrimidine biosynthesis.svg

The starting material is 5-aminoimidazole ribotide, which undergoes a rearrangement reaction via radical intermediates which incorporate the blue, green and red fragments shown into the product.