5′-Phosphoribosylformylglycinamidine
# 5′-Phosphoribosylformylglycinamidine

5′-Phosphoribosylformylglycinamidine (or FGAM) is a biochemical intermediate in the formation of purine nucleotides via inosine-5-monophosphate, and hence is a building block for DNA and RNA. The vitamins thiamine and cobalamin also contain fragments derived from FGAM.

The compound is biosynthesized from phosphoribosyl-N-formylglycineamide (FGAR) which is converted to an amidine by the action of phosphoribosylformylglycinamidine synthase (EC 6.3.5.3), transferring an amino group from glutamine in a reaction that also requires ATP:

    FGAR + ATP + glutamine + $H_2O$ → FGAM + ADP + glutamate + Pi

The biosynthesis pathway next converts FGAM to 5-aminoimidazole ribotide (AIR) by the action of AIR synthetase (EC 6.3.3.1) which uses ATP to activate the terminal carbonyl group to attack by the nitrogen atom at the anomeric center:

    FGAM + ATP → AIR + ADP + Pi + $H^+$
