Skip to main content
padlock icon - secure page this page is secure

Free Content Identification and functional analysis of a prokaryotic‐type aspartate aminotransferase: implications for plant amino acid metabolism

Download Article:
In this paper, we report the identification of genes from pine (PpAAT), Arabidopsis (AtAAT) and rice (OsAAT) encoding a novel class of aspartate aminotransferase (AAT, EC in plants. The enzyme is unrelated to other eukaryotic AATs from plants and animals but similar to bacterial enzymes. Phylogenetic analysis indicates that this prokaryotic‐type AAT is closely related to cyanobacterial enzymes, suggesting it might have an endosymbiotic origin. Interestingly, most of the essential residues involved in the interaction with the substrate and the attachment of pyridoxal phosphate cofactor in the active site of the enzyme were conserved in the deduced polypeptide. The polypeptide is processed in planta to a mature subunit of 45 kDa that is immunologically distinct from the cytosolic, mitochondrial and chloroplastic isoforms of AAT previously characterized in plants. Functional expression of PpAAT sequences in Escherichia coli showed that the processed precursor is assembled into a catalytically active homodimeric holoenzyme that is strictly specific for aspartate. These atypical genes are predominantly expressed in green tissues of pine, Arabidopsis and rice, suggesting a key role of this AAT in nitrogen metabolism associated with photosynthetic activity. Moreover, immunological analyses revealed that the plant prokaryotic‐type AAT is a nuclear‐encoded chloroplast protein. This implies that two plastidic AAT co‐exist in plants: a eukaryotic type previously characterized and the prokaryotic type described here. The respective roles of these two enzymes in plant amino acid metabolism are discussed.
No References
No Citations
No Supplementary Data
No Article Media
No Metrics

Keywords: amino acid metabolism; aspartate aminotransferase; chloroplast; prokaryotic‐type enzyme

Document Type: Research Article

Affiliations: Departamento de Biología Molecular y Bioquímica, Instituto Andaluz de Biotecnología, Unidad Asociada UMA-CSIC, Campus Universitario de Teatinos, Universidad de Málaga, 29071-Málaga, Spain

Publication date: May 1, 2006

  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more