7-Carboxy-7-deazaguanine synthase (EC 4.3.99.3, 7-carboxy-7-carbaguanine synthase, queE (gene)) is an enzyme with systematic name 6-carboxy-5,6,7,8-tetrahydropterin ammonia-lyase. This enzyme catalyses the following chemical reaction
The enzyme is a member of the superfamily of S-adenosyl-<small>L</small>-methionine-dependent radical enzymes.