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Query: EC:3.5.1.1 (asparaginase)
 2,695 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Characterization of Arabidopsis serine:glyoxylate aminotransferase, AGT1, as an asparagine aminotransferase. 2309 2

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.
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PMID:Identification and characterization of omega-amidase as an enzyme metabolically linked to asparagine transamination in Arabidopsis. 2446 Dec 28