title: Recombinant expression, purification, and characterization of three isoenzymes of aspartate aminotransferase from Arabidopsis thaliana.
abstract: Five different genes encoding isoenzymes of aspartate aminotransferase (AAT) have been identified in the plant Arabidopsis thaliana. cDNA sequences encoding three of these AAT isoenzymes, asp1 (mitochondrial), asp2 (cytosolic), and asp5 (plastid), were manipulated into bacterial expression vectors and the recombinant proteins expressed were purified from liquid culture using conventional methods. Yields of the purified isoenzymes varied from 11.5 mg/g wet wt cells (AAT5) to 0.95 mg/g wet wt cells (AAT2), an improvement of more than 1000-fold over typical yields of native isoenzymes obtained from plant tissues of other species. Analysis of the recombinant proteins on denaturing PAGE gels indicated subunit Mrs of between 44 and 45 K. Kinetic parameters (Km and kcat) obtained for all four substrates (aspartate, alpha-ketoglutarate, glutamate, and oxaloacetate) were consistent with values obtained for native AAT isoenzymes from other plant species. Further characterization of the purified recombinant enzymes alongside native enzymes from A. thaliana leaf tissue on AAT activity gels confirmed the identity of asp1 and asp2 as the mitochondrial and cytosolic AAT genes but indicated that asp5 may encode an amyloplastic rather than the chloroplastic enzyme.
authors.affiliation: Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, United Kingdom. s.wilkie@ucl.ac.uk
authors.forename: S E
authors.initials: SE
authors.lastname: Wilkie
authors.forename: M J
authors.initials: MJ
authors.lastname: Warren
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D001219:Aspartate Aminotransferases / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D001483:Base Sequence; D017931:DNA Primers / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics*; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D017931:DNA Primers; D007527:Isoenzymes; D010940:Plant Proteins; D011994:Recombinant Proteins; D001219:Aspartate Aminotransferases