The ureide-degrading reactions of purine ring catabolism employ three amidohydrolases and one aminohydrolase in Arabidopsis, soybean, and rice.
Several ureides are intermediates of purine base catabolism, releasing nitrogen from the purine nucleotides for reassimilation into amino acids. In some legumes like soybean (Glycine max), ureides are used for nodule-to-shoot translocation of fixed nitrogen. Four enzymes of Arabidopsis (Arabidopsis thaliana), (1) allantoinase, (2) allantoate amidohydrolase (AAH), (3) ureidoglycine aminohydrolase, and (4) ureidoglycolate amidohydrolase (UAH), catalyze the complete hydrolysis of the ureide allantoin in vitro. However, the metabolic route in vivo remains controversial. Here, in growth and metabolite analyses of Arabidopsis mutants, we demonstrate that these enzymes are required for allantoin degradation in vivo. Orthologous enzymes are present in soybean, encoded by one to four gene copies. All isoenzymes are active in vitro, while some may be inefficiently translated in vivo. Surprisingly, transcript and protein amounts are not significantly regulated by nitrogen fixation or leaf ureide content. A requirement for soybean AAH and UAH for ureide catabolism in leaves has been demonstrated by the use of virus-induced gene silencing. Functional AAH, ureidoglycine aminohydrolase, and UAH are also present in rice (Oryza sativa), and orthologous genes occur in all other plant genomes sequenced to date, indicating that the amidohydrolase route of ureide degradation is universal in plants, including mosses (e.g. Physcomitrella patens) and algae (e.g. Chlamydomomas reinhardtii).
Freie Universität Berlin, Dahlem Centre of Plant Sciences, Department of Plant Biochemistry, 14195 Berlin, Germany.
Andrea K
AK
Werner
Nieves
N
Medina-Escobar
Monika
M
Zulawski
Imogen A
IA
Sparkes
Feng-Qiu
FQ
Cao
Claus-Peter
CP
Witte
D000581:Amidohydrolases / Q000378:metabolism*; D000619:Aminohydrolases / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000254:growth & development; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D005816:Genetic Complementation Test; D007700:Kinetics; D055432:Metabolomics; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D012275:Oryza / Q000201:enzymology*; D010940:Plant Proteins / Q000378:metabolism; D011687:Purines / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013025:Glycine max / Q000201:enzymology* / Q000235:genetics; D013347:Subcellular Fractions / Q000201:enzymology; D014508:Urea / Q000031:analogs & derivatives / Q000378:metabolism*
D010940:Plant Proteins; D011687:Purines; D012333:RNA, Messenger; C024081:allantoic acid; D014508:Urea; D000581:Amidohydrolases; D000619:Aminohydrolases; C030985:purine