tailieunhanh - Báo cáo khoa học: Purification and kinetic analysis of the two recombinant arogenate dehydrogenase isoforms of Arabidopsis thaliana

The present study reports the first purification and kinetic characterization of two plant arogenate dehydrogenases (EC ), an enzyme that catalyses the oxidative decarboxylation of arogenate into tyrosine in presence of NADP. The twoArabidopsis thalianaarogenate dehy-drogenases TyrAAT1 and TyrAAT2 were overproduced in Escherichia coliand purified to homogeneity. Bio-chemical comparison of the two forms revealed that at low substrate concentration TyrAAT1 is four times more efficient in catalyzing the arogenate dehydrogenase reac-tion than TyrAAT2. . | Eur. J. Biochem. 269 4753-4761 2002 FEBS 2002 doi Purification and kinetic analysis of the two recombinant arogenate dehydrogenase isoforms of Arabidopsis thaliana Pascal Rippert and Michel Matringe Laboratoire Mixte CNRSjINRAjBayer CropScience UMR 1932 Lyon France The present study reports the first purification and kinetic characterization of two plant arogenate dehydrogenases EC an enzyme that catalyses the oxidative decarboxylation of arogenate into tyrosine in presence of NADP. The two Arabidopsis thaliana arogenate dehydrogenases TyrAAT1 and TyrAAT2 were overproduced in Escherichia coli and purified to homogeneity. Biochemical comparison of the two forms revealed that at low substrate concentration TyrAAT1 is four times more efficient in catalyzing the arogenate dehydrogenase reaction than TyrAAT2. Moreover TyrAAT2 presents a weak prephenate dehydrogenase activity whereas Tyr-AAT1 does not. The mechanism of the dehydrogenase reaction catalyzed by these two forms has been investigated using steady-state kinetics. For both enzymes steady-state velocity patterns are consistent with a rapid equilibrium random mechanism in which two dead-end complexes E-NADPH-arogenate and E-NADP-tyro-sine are formed. Keywords Arabidopsis thaliana tyrosine biosynthesis arogenate dehydrogenase isoforms enzymatic properties. Archae eubacteria plants and fungi are capable of synthesizing de novo the three aromatic amino acids phenylalanine tyrosine and tryptophan. The enzymes catalyzing these reactions are thus potentially useful targets for the development of new antibiotics fungicides and herbicides. The broad-spectrumherbicide glyphosate that inhibits 5-enolpyruvyl shikimate 3-phosphate synthase is the best example of this potential 1 . For the biosynthesis of phenylalanine and tyrosine alternative routes exist in nature Fig. 1 . In organisms such as Saccharomyces cerevisiae or Escherichia coli 2 3 phenylpyruvate and .

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