Heterocyclic nitrogen compounds may serve as nitrogen sources or nitrogen transport compounds in plants that are not able to fix nitrogen. This family represents ureide permease, a transporter of a wide spectrum of oxo derivatives of heterocyclic nitrogen compounds, including allantoin, uric acid and xanthine; it has 10 putative transmembrane domains with a large cytosolic central domain containing a 'Walker A' motif. Ureide permease is likely to transport other purine degradation products when nitrogen sources are low. Transport is dependent on glucose and a proton gradient [1]. The family is found in bacteria, plants and yeast. These transporters are constituted of two sets of 5xTMs.

1: A novel superfamily of transporters for allantoin and other oxo derivatives of nitrogen heterocyclic compounds in Arabidopsis. Desimone M, Catoni E, Ludewig U, Hilpert M, Schneider A, Kunze R, Tegeder M, Frommer WB, Schumacher K; Plant Cell. 2002;14:847-856. PMID:11971139