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Peroxisomal alanine : glyoxylate aminotransferase (AGT1) is a photorespiratory enzyme with multiple substrates in Arabidopsis thaliana

Peroxisomal alanine : glyoxylate aminotransferase (AGT1) is a photorespiratory enzyme with... At least two glyoxylate aminotransferases are hypothesized to participate in the steps of photorespiration located in peroxisomes. Until recently, however, genes encoding these enzymes had not been identified. We describe the isolation and characterization of an alanine : glyoxylate aminotransferase (AGT1, formerly AGT) cDNA from Arabidopsis thaliana. Southern blot analysis confirmed that Arabidopsis AGT1 is encoded by a single gene. Homologs of this class IV aminotransferase are also known in other plants, animals, and methylotrophic bacteria, suggesting an ancient evolutionary origin of this enzyme. AGT1 transcripts were present in all tissues of Arabidopsis, but were most abundant in green, leafy tissues. Purified, recombinant Arabidopsis AGT1 expressed in Escherichia coli catalyzed three transamination reactions using the following amino donor : acceptor combinations: alanine : glyoxylate, serine : glyoxylate, and serine : pyruvate. AGT1 had the highest specific activity with the serine : glyoxylate transamination, and apparent Km measurements indicate that this is the preferred in vivo reaction. In vitro import experiments and subcellular fractionations localized AGT1 to peroxisomes. Sequence analysis of the photorespiratory sat mutants revealed a single nucleotide substitution in the AGT1 gene from these plants. This transition mutation is predicted to result in a proline‐to‐leucine substitution at residue 251 of AGT1. When this mutation was engineered into the recombinant AGT1 protein, enzymatic activity using all three donor : acceptor pairs was abolished. We conclude that Arabidopsis AGT1 is a peroxisomal photorespiratory enzyme that catalyzes transamination reactions with multiple substrates. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Plant Journal Wiley

Peroxisomal alanine : glyoxylate aminotransferase (AGT1) is a photorespiratory enzyme with multiple substrates in Arabidopsis thaliana

The Plant Journal , Volume 25 (5) – Mar 1, 2001

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References (78)

Publisher
Wiley
Copyright
Copyright © 2001 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0960-7412
eISSN
1365-313X
DOI
10.1046/j.1365-313x.2001.00961.x
Publisher site
See Article on Publisher Site

Abstract

At least two glyoxylate aminotransferases are hypothesized to participate in the steps of photorespiration located in peroxisomes. Until recently, however, genes encoding these enzymes had not been identified. We describe the isolation and characterization of an alanine : glyoxylate aminotransferase (AGT1, formerly AGT) cDNA from Arabidopsis thaliana. Southern blot analysis confirmed that Arabidopsis AGT1 is encoded by a single gene. Homologs of this class IV aminotransferase are also known in other plants, animals, and methylotrophic bacteria, suggesting an ancient evolutionary origin of this enzyme. AGT1 transcripts were present in all tissues of Arabidopsis, but were most abundant in green, leafy tissues. Purified, recombinant Arabidopsis AGT1 expressed in Escherichia coli catalyzed three transamination reactions using the following amino donor : acceptor combinations: alanine : glyoxylate, serine : glyoxylate, and serine : pyruvate. AGT1 had the highest specific activity with the serine : glyoxylate transamination, and apparent Km measurements indicate that this is the preferred in vivo reaction. In vitro import experiments and subcellular fractionations localized AGT1 to peroxisomes. Sequence analysis of the photorespiratory sat mutants revealed a single nucleotide substitution in the AGT1 gene from these plants. This transition mutation is predicted to result in a proline‐to‐leucine substitution at residue 251 of AGT1. When this mutation was engineered into the recombinant AGT1 protein, enzymatic activity using all three donor : acceptor pairs was abolished. We conclude that Arabidopsis AGT1 is a peroxisomal photorespiratory enzyme that catalyzes transamination reactions with multiple substrates.

Journal

The Plant JournalWiley

Published: Mar 1, 2001

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