Carboxyaminoimidazole ribotide (CAIR) is a metabolite of E. coli. Carboxyaminoimidazole ribotide can be used to detect distinctive features of E. coli PurE active site and synthesis fungal de novo purine.
References:
[1]. Firestine SM, et al. Biochemical role of the Cryptococcus neoformans ADE2 protein in fungal de novo purine biosynthesis. Arch Biochem Biophys. 1998 Mar 1;351(1):123-34.