The enzyme is composed of two parts, a glutaminase (PabA in Escherichia coli) and an aminotransferase (PabB). In the absence of PabA and glutamine (but in the presence of Mg2+), PabB can convert ammonia and chorismate into 4-amino-4-deoxychorismate. PabA converts glutamine into glutamate only in the presence of stoichiometric amounts of PabB. In many organisms, including plants, the genes encoding the two proteins have fused to encode a single bifunctional protein. This enzyme is coupled with EC 4.1.3.38, aminodeoxychorismate lyase, to form 4-aminobenzoate. cf. EC 2.6.1.123, 4-amino-4-deoxychorismate synthase (2-amino-4-deoxychorismate-forming).
non linear production of PABA in the ADC synthase-ADC lyase-coupled reaction system, at different glutamine and chorismate concentrations, with limiting PabB
omega-amino group of K274 adds to chorismate at C2, leading to elimination of the C4 hydroxyl in an SN2'' displacement reaction. After attack of ammonia to intermediate, another SN2'' displacement expels K274 and forms aminodeoxychorismate
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SYSTEMATIC NAME
IUBMB Comments
chorismate:L-glutamine aminotransferase
The enzyme is composed of two parts, a glutaminase (PabA in Escherichia coli) and an aminotransferase (PabB). In the absence of PabA and glutamine (but in the presence of Mg2+), PabB can convert ammonia and chorismate into 4-amino-4-deoxychorismate. PabA converts glutamine into glutamate only in the presence of stoichiometric amounts of PabB. In many organisms, including plants, the genes encoding the two proteins have fused to encode a single bifunctional protein. This enzyme is coupled with EC 4.1.3.38, aminodeoxychorismate lyase, to form 4-aminobenzoate. cf. EC 2.6.1.123, 4-amino-4-deoxychorismate synthase (2-amino-4-deoxychorismate-forming).
heterodimer of chorismate aminating subunit and glutamine amidotransferase subunit. Mass of glutamine amidotransferase subunit is 50969 Da, as determined by electrospray mass spectrometry
mutant displaying anthranilate synthase activity, the kcat/Kchoris value for anthranilate formation is 25% of the wild-type aminodeoxychorismate synthase value for 4-amino-4-deoxychorismate production
protamine sulfate precipitation, ammonium sulfate fractionation, chromatography on Sephacryl S-200, chromatography on DEAE-Sephacel and chromatography on dye-agarose
conversion of aminodeoxychorismate synthase into anthranilate synthase employing a bioinformatics method for predicting mutations required to functionally interconvert homologous enzymes. Complementation of an anthranilate synthase-deficient strain of Escherichia coli grown on minimal medium leads to several aminodeoxychorismate synthase mutants that allow growth in 6 days compared to 2 days for wild-type anthranilate synthase. The purified mutant enzymes catalyze the conversion of chorismate to anthranilate at rates that are about 50% of the rate of wild-type aminodeoxychorismate synthase-catalyzed conversion of chorismate to aminodeoxychorismate. The residues mutated do not contact the substrate
p-Aminobenzoate synthesis in Escherichia coli: purification and characterization of PabB as aminodeoxychorismate synthase and enzyme X as aminodeoxychorismate lyase
Conversion of aminodeoxychorismate synthase into anthranilate synthase with Janus mutations: mechanism of pyruvate elimination catalyzed by chorismate enzymes