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.
Phytochemistry. 2013 Jan;85:30-5. doi: 10.1016/j.phytochem.2012.09.017. Epub 2012 Oct 22.
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.
天冬酰胺（Asn）是一种主要的氮形式，被运输到汇组织。先前的研究结果表明，缺乏天冬酰胺酶活性的拟南芥突变体发育相对正常，这突出了其他类型的天冬酰胺代谢酶可能存在代偿作用。先前对大麦和烟草突变体的研究表明，天冬酰胺转氨酶活性与光呼吸酶丝氨酸（Ser）：乙醛酸转氨酶有关。该酶由拟南芥中的 AGT1 编码。从大肠杆菌中纯化的带有 N 端 His 标签的重组 AGT1 用 Ser、丙氨酸（Ala）和 Asn 作为氨基酸供体，以及乙醛酸、丙酮酸和羟丙酮酸作为有机酸受体进行了表征。AGT1 与 Asn 的 V(max)比与 Ser 或 Ala 高约 5 到 20 倍。因此，与其他两种氨基酸相比，AGT1 与 Asn 的催化效率（V(max)/K(m)）略高。在用 20mM Asn 处理 10 天大的幼苗根系 2 小时后，AGT1 转录本水平提高了 2 倍。在此处理过程中，根系中天冬酰胺的浓度提高了约 5 倍。这些结果表明，AGT1 参与了拟南芥中天冬酰胺的代谢。
