In eubacteria, fungi and plants, this enzyme, along with EC 188.8.131.52
, 5-(carboxyamino)imidazole ribonucleotide synthase, is required to carry out the single reaction catalysed by EC 184.108.40.206
, phosphoribosylaminoimidazole carboxylase, in vertebrates . In the absence of EC 220.127.116.11
, phosphoribosylaminoimidazolesuccinocarboxamide synthase, the reaction is reversible . The substrate is readily converted into 5-amino-1-(5-phospho-D-ribosyl)imidazole by non-enzymic decarboxylation .