title: Characterization of Arabidopsis serine:glyoxylate aminotransferase, AGT1, as an asparagine aminotransferase.
abstract: Asparagine (Asn) is a major form of nitrogen transported to sink tissues. Results from a previous study have shown that an Arabidopsis mutant lacking asparaginase activity develops relatively normally, highlighting a possible compensation by other types of asparagine metabolic enzymes. Prior studies with barley and tobacco mutants have associated Asn aminotransferase activity with the photorespiratory enzyme, serine (Ser):glyoxylate aminotransferase. This enzyme is encoded by AGT1 in Arabidopsis thaliana. Recombinant N-terminal His-tagged AGT1 purified from Escherichia coli was characterized with Ser, alanine (Ala) and Asn as amino acid donors and glyoxylate, pyruvate and hydroxypyruvate as organic acid acceptors. The V(max) of AGT1 with Asn was higher than with Ser or Ala by ca. 5- to 20-fold. As a result, the catalytic efficiency (V(max)/K(m)) was slightly higher with Asn than with the two other amino acids. In the roots of 10-day-old seedlings treated for 2h with 20mM Asn, the AGT1 transcript levels were raised by 2-fold. During this treatment, the concentration of Asn in root was raised by ca. 5-fold. These results suggest that AGT1 is involved in Asn metabolism in Arabidopsis.
authors.affiliation: Department of Biology, University of Western Ontario, London, ON, Canada N6A 5B7; Agriculture and Agri-Food Canada, Genomics and Biotechnology, Southern Crop Protection and Food Research Centre, 1391 Sandford St, London, ON, Canada N5V 4T3.
authors.forename: Qianyi
authors.initials: Q
authors.lastname: Zhang
authors.forename: Jamie
authors.initials: J
authors.lastname: Lee
authors.forename: Sudhakar
authors.initials: S
authors.lastname: Pandurangan
authors.forename: Matthew
authors.initials: M
authors.lastname: Clarke
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Pajak
authors.forename: Frédéric
authors.initials: F
authors.lastname: Marsolais
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001216:Asparagine / Q000378:metabolism; D000637:Transaminases / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D001216:Asparagine; D000637:Transaminases; C022636:serine-glyoxylate aminotransferase