Back to Search
Start Over
Folate synthesis in plants: purification, kinetic properties, and inhibition of aminodeoxychorismate synthase
- Source :
- Biochemical Journal, Biochemical Journal, 2006, 396, pp.157-162. ⟨10.1042/BJ20051851⟩, Biochemical Journal, Portland Press, 2006, 396, pp.157-162. ⟨10.1042/BJ20051851⟩
- Publication Year :
- 2006
- Publisher :
- HAL CCSD, 2006.
-
Abstract
- pABA (p-aminobenzoate) is a precursor of folates and, besides esterification to glucose, has no other known metabolic fate in plants. It is synthesized in two steps from chorismate and glutamine, the first step being their conversion into glutamate and ADC (4-aminodeoxychorismate). In Escherichia coli, two proteins forming a heterodimeric complex are required for this reaction, but, in plants and lower eukaryotes, a single protein is involved. The Arabidopsis enzyme was expressed in E. coli and was purified to homogeneity. The monomeric enzyme (95 kDa) catalyses two reactions: release of NH3 from glutamine (glutaminase activity) and substitution of NH3 for the hydroxy group at position 4 of chorismate (ADC synthase activity). The kinetic parameters of the plant enzyme are broadly similar to those of the bacterial complex, with Km values for glutamine and chorismate of 600 and 1.5 μM respectively. As with the bacterial enzyme, externally added NH3 was a very poor substrate for the plant enzyme, suggesting that NH3 released from glutamine is preferentially channelled to chorismate. The glutaminase activity could operate alone, but the presence of chorismate increased the efficiency of the reaction 10-fold, showing the interdependency of the two domains. The plant enzyme was inhibited by dihydrofolate and its analogue methotrexate, a feature never reported for the prokaryotic system. These molecules were inhibitors of the glutaminase reaction, competitive with respect to glutamine (Ki values of 10 and 1 μM for dihydrofolate and methotrexate respectively). These findings support the view that the monomeric ADC synthase is a potential target for antifolate drugs.
- Subjects :
- 0106 biological sciences
Folate
Chorismic Acid
Glutamine
plant
01 natural sciences
Biochemistry
Glutaminase activity
Substrate Specificity
enzymatic inhibitor
Aminobenzoate
chemistry.chemical_compound
Pyruvic Acid
Carbon-Nitrogen Ligases
chemistry.chemical_classification
0303 health sciences
C1 metabolism
biology
Glutaminase
vitamin
4-Aminobenzoic Acid
Research Article
Aminodeoxychorismate synthase
Stereochemistry
antifolate drug
Recombinant Fusion Proteins
dihydrofolate
methotrexate
03 medical and health sciences
Folic Acid
Biosynthesis
P aminobenzoate
Escherichia coli
aminodeoxychorismate synthase
[SDV.BBM]Life Sciences [q-bio]/Biochemistry, Molecular Biology
Molecular Biology
Transaminases
030304 developmental biology
Arabidopsis Proteins
Substrate (chemistry)
glutaminase
Cell Biology
enzyme
Enzyme
chemistry
kinetics
biology.protein
biosynthesis
010606 plant biology & botany
Subjects
Details
- Language :
- English
- ISSN :
- 02646021 and 14708728
- Database :
- OpenAIRE
- Journal :
- Biochemical Journal, Biochemical Journal, 2006, 396, pp.157-162. ⟨10.1042/BJ20051851⟩, Biochemical Journal, Portland Press, 2006, 396, pp.157-162. ⟨10.1042/BJ20051851⟩
- Accession number :
- edsair.doi.dedup.....b69dcf4a0c7d50d39144831507740c0b