N-acetyl glutamate kinase from Daucus carota suspension cultures: embryogenic expression profile, purification and characterization

• Published in: Plant physiology and biochemistry 2005-09, Vol.43 (9), p.854-861
• Main Authors: Lohmeier-Vogel, Elke M., Loukanina, Natalia, Ferrar, Tony S., Moorhead, Greg B.G., Thorpe, Trevor A.
• Format: Article
• Language: English
• Subjects: Arabidopsis thaliana; Arginine; Biological and medical sciences; Daucus carota; Daucus carota - cytology; Daucus carota - enzymology; Electrophoresis, Polyacrylamide Gel; Enzymes; Fundamental and applied biological sciences. Psychology; Gene Expression Profiling; Metabolism; N-acetylglutamte kinase; NAGK; Ornithine cycle; Phosphotransferases (Carboxyl Group Acceptor) - genetics; Phosphotransferases (Carboxyl Group Acceptor) - isolation & purification; Phosphotransferases (Carboxyl Group Acceptor) - metabolism; Plant physiology and development; Seeds - enzymology; Seeds - growth & development; Somatic embryogenesis
• ISSN: 0981-9428; 1873-2690
• DOI: 10.1016/j.plaphy.2005.07.009

In Daucus carota, N-acetylglutamate-5-phosphotransferase (NAGK; E.C. 2.7.2.8) specific activity was shown to correlate with the progression of somatic embryogenesis and was highest in the latter stages, where growth was most rapid. The enzyme was subsequently purified greater than 1200-fold using heat treatment, ammonium sulfate fractionation, gel filtration, anion exchange and dye ligand chromatography. Carrot NAGK was shown to have a subunit molecular weight of 31 kDa and form a hexamer. The Kms for NAG and ATP are 5.24 and 2.11 mM, respectively. Arginine (Arg) is a K-type allosteric inhibitor of the enzyme, and Hill coefficients in the order of 5 in the presence of Arg suggest that the enzyme is highly cooperative. D. carota NAGK does not bind to Arabidopsis thaliana PII affinity columns, nor does the A. thaliana PII increase NAGK specific activity, indicating its cellular location is probably different.