Identification and characterization of omega-amidase as an enzyme metabolically linked to asparagine transamination in Arabidopsis.
In higher plants, asparagine (Asn) is a major form of organic nitrogen used for transport and storage. There are two pathways of Asn metabolism, involving asparaginase and Asn aminotransferase. The enzyme serine:glyoxylate aminotransferase encoded by AGT1 has been identified as an asparagine aminotransferase in Arabidopsis. The product of asparagine transamination, alpha-ketosuccinamate, can be hydrolyzed by the enzyme omega-amidase to form oxaloacetate and ammonia. A candidate gene was identified in Arabidopsis based on its sequence similarity with mouse omega-amidase. Recombinant omega-amidase exhibited comparable catalytic activities with alpha-hydroxysuccinamate, alpha-ketosuccinamate and alpha-ketoglutaramate, the product of glutamine transamination. A mutant with a T-DNA inserted in the first exon accumulated alpha-ketosuccinamate and alpha-hydroxysuccinamate as compared with wild-type, both under control conditions and after treatment with Asn. Treatment with Asn led to decreased transcript levels of omega-amidase in root, while transcript levels of AGT1 are increased under these conditions, suggesting that excess Asn may lead to the accumulation of alpha-ketosuccinamate and alpha-hydroxysuccinamate.
Department of Biology, University of Western Ontario, London, ON N6A 5B7, Canada; Agriculture and Agri-Food Canada, Genomics and Biotechnology, Southern Crop Protection and Food Research Centre, 1391 Sandford St., London, ON N5V 4T3, Canada.
Qianyi
Q
Zhang
Department of Biology, University of Western Ontario, London, ON N6A 5B7, Canada; Agriculture and Agri-Food Canada, Genomics and Biotechnology, Southern Crop Protection and Food Research Centre, 1391 Sandford St., London, ON N5V 4T3, Canada. Electronic address: Frederic.Marsolais@agr.gc.ca.
Frédéric
F
Marsolais
D000581:Amidohydrolases / Q000378:metabolism*; D000586:Amination; D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D001216:Asparagine / Q000378:metabolism*
D001216:Asparagine; D000581:Amidohydrolases; C047679:omega-amidase
Alpha-hydroxysuccinamate; Alpha-ketoglutaramate; Alpha-ketosuccinamate; Arabidopsis thaliana; Asparagine; Cruciferae; Omega-amidase