page_title: Formylation
section_title: Mechanism
hierarchical_section_title: Formylation / Formylation reactions in biology / Formylation reactions in purine biosynthesis / AICAR transformylase / Mechanism
caption_attribution_description: English: mechanism of enzyme AICAR transformylase
context_page_description: In biochemistry, the addition of a formyl functional group is termed formylation. A formyl functional group consists of a carbonyl bonded to hydrogen. When attached to an R group, a formyl group is called an aldehyde.
  Formylation has been identified in several critical biological processes. Methionine was first discovered to be formylated in E. coli by Marcker and Sanger in 1964 and was later identified to be involved in the initiation of protein synthesis in bacteria and organelles. The formation of N-formylmethionine is catalyzed by the enzyme methionyl-tRNAᴹᵉᵗ transformylase. Additionally, two formylation reactions occur in the de novo biosynthesis of purines. These reactions are catalyzed by the enzymes glycinamide ribonucleotide transformylase and 5-aminoimidazole-4-carboxyamide ribotide transformylase. More recently, formylation has been discovered to be a histone modification, which may modulate gene expression.
context_section_description: The amine on AICAR is much less nucleophillic than its counterpart on GAR due to delocalization of electrons in AICAR through conjugation. Therefore, the N5 nucleophile of AIRCAR must be activated for the formylation reaction to occur. Histidine 268 and Lysine 267 have been found to be essential for catalysis and are conserved in all AICAR transformylase. Histidine 268 is involved in deprotonation of the N5 nucleophile of AICAR, whereas Lysine 267 is proposed to stabilize the tetrahedral intermediate.
caption: Mechanism catalyzed by AICAR Transformylase
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