Purines · reaction 2 of 2

PRPP + Glutamine + Water → 5-Phosphoribosylamine + Glutamate + Pyrophosphate

Glutamine-PRPP amidotransferase EC 2.4.2.14

Swaps the pyrophosphate for a nitrogen that comes from glutamine. It is the first step unique to purines and the one that decides how many are made: the pathway's own products slow it down when there are too many.

irreversible
Cytosol

in depth

ΔG°′: not documented
Inhibited by: AMP
Inhibited by: GMP
Location: Cytosol

Fun fact

Unlike pyrimidines, whose ring is assembled separately and then attached to the sugar, the purine is built piece by piece on top of ribose. This is the first brick, and the eight steps that raise the rest of the ring are still to be written in this atlas.