Anthranilate synthase

Figure 1. Schematic outline of various products and associated enzymes from the shikimate and phenolic pathways in plants (and some microorganisms). Enzymes (1) 3-deoxy-2-oxo-D-arabino-heptulosate-7-phosphate synthase (2) 5-dehydroquinate synthase (3) shikimate dehydrogenase (4) shikimate kinase (5) 5-enol-pyruvylshikimate-3-phosphate synthase (6) chorismate synthase (7) chorismate mutase (8) prephenate dehydrogenase (9) tyrosine aminotransferase (10) prephenate dehydratase (11) phenylalanine aminotransferase (12) anthranilate synthase (13) tryptophan synthase (14) phenylalanine ammonia-lyase (15) tyrosine ammonia-lyase and (16) polyphenol oxidase. (From ACS Symposium Series No. 181, 1982) (62).

This enzyme [EC 2.4.2.18], also referred to as phospho-ribosyl-anthranilate pyrophosphorylase, catalyzes the reaction of anthranilate with phosphoribosylpyrophos-phate to produce A-5 -phosphoribosylanthranilate and pyrophosphate. In certain species, this enzyme is part of a multifunctional protein, together with one or more other components of the system for the biosynthesis of tryptophan (i.e., indole-3-glycerol-phosphate synthase, anthranilate synthase, tryptophan synthase, and phos-phoribosylanthranilate isomerase). 

Figure 1. Hypothetical mechanism for shuttling of intermediates of the common aromatic pathway between plastidic and cytosolic compartments. Enzymes denoted with an asterisk (DAHP synthase-Co, chorismate mutase-2, and cytosolic anthranilate synthase) have been demonstrated to be isozymes located in the cytosol. DAHP molecules from the cytosol are shown to be shuttled into the plastid compartment in exchange for EPSP molecules synthesized within the plastid. Abbreviations C3, phosphoenolpyruvate C4, erythrose 4-P DAHP, 3-deoxy-D-arabino-heptulosonate 7-phosphate EPSP, 5-enolpyruvylshikimate 3-phosphate CHA, chorismate ANT, anthranilate TRP, L-tryptophan PPA, prephenate AGN, L-arogenate TYR, L-tyrosine and PHE, L-phenylalanine.

Of the separately compartmented isozyme pairs that exist for DAHP synthase, chorismate mutase, and anthranilate synthase, each isozyme member of a given pair has different properties of regulation and other distinctive characteristics (see Tables I and II). This suggests a high probability that each isozyme is the gene product of a different gene. 

Peebles, C. A. M., Hong, S. B., Gibson, S. L, Shanks, J. V. and San, K. Y. 2005. Transient effects of overexpressing anthranilate synthase alpha and beta subunits in Catharanthus roseus hairy roots. Biotechnology Progress, 21 1572-1576. 

During the conversion of anthranilate to tryptophan, two additional carbon atoms must be incorporated to form the indole ring. These are derived from phosphoribosyl pyrophosphate (PRPP) which is formed from ribose 5-phosphate by transfer of a pyro-phospho group from ATP.60 61 The - OH group on the anomeric carbon of the ribose phosphate displaces AMP by attack on Pp of ATP (Eq. 25-5). In many organisms the enzyme that catalyzes this reaction is fused to subunit II of anthranilate synthase.62 PRPP is also the donor of phosphoribosyl groups for biosynthesis of histidine (Fig. 25-13) and of nucleotides (Figs. 

The first specific step in tryptophan biosynthesis is the glutamine-dependent conversion of chorismate to the simple aromatic compound anthranilate. Like most other glutamine-dependent reactions, the reaction can also occur with ammonia as the source of the amino group. However, high concentrations of ammonia are required. Thus far, almost all the anthranilate synthases examined have the glutamine amidotransferase activity (component II) and the choris-mate-to-anthranilate activity (component I) on separate proteins. 

Metabolite flow to tryptophan is controlled by inhibition of anthranilate synthase by tryptophan (see fig. 

Biosynthetic processes Elongation of RNA or DNA chains Other synthetic routes RNA polymerase I DNA polymerase Poly(ADP-ribose)polymerase Carbamoyl phosphate synthetase Anthranilate synthase-phosphoribosyl transferase Glycogen synthetase Methionyl-tRNA synthetase ATP phosphoribosyl transferase Zn2+... 

The first two steps in the biosynthesis of tryptophan in Salmonella typhimurium involve the enzyme complex anthranilate synthase-phosphoribosyltransferase, which is a tetramer having two subunits of each enzyme. The anthranilate synthase catalyzes reaction (7) and the phos-phoribosyltransferase catalyzes two reactions the N-terminal portion cleaves glutamine to glutamate giving NH3 for the anthranilate synthase, while the C-terminal portion catalyzes reaction (8).3,1,312 All these reactions require M2+ cations. Orotate phosphoribosyltransferase binds four Mn2+ ions in a cooperative fashion kinetic data have been interpreted in a scheme where both metal-free and metal-containing enzyme catalyze the reaction.313... 

Chorismic acid (26), thus, represents the first divergence point of pyocyanin from other biosynthetic pathways. The first authentic pyocyanin biosynthetic enzyme is PhzE, which has sequence similarity to anthranilate synthases, which generate anthranilate from chorismate. PhzE is thought to catalyze the conversion of chorismic acid (26) to amine 165. Compound 165 is in turn a substrate for PhzD, an isochorismatase that catalyzes the hydrolysis of the vinyl ether to 166 and pyruvate [188, 189],... 

Fig. 3. Biosynthesis of TIAs in C. roseus. Solid arrows indicate single enzymatic conversions, whereas dashed arrows indicate multiple enzymatic conversions. AS Anthranilate synthase, DXS D-l-deoxyxylulose 5-phosphate synthase G10H geraniol 10-hydroxylase CPR cytochrome P450 reductase TDC tryptophan decarboxylase STR strictosidine synthase SGD strictosidine /1-D-glucosidase D4H desacetoxyvindoline 4-hydroxylase DAT acetyl-CoA 4-O-deacetylvindoline 4-O-acetyl transferase. Genes regulated by ORCA3 are underlined. Reprinted with permission from [91]. Copyright (2000) American Association for the Advancement of Science...

For the aromatic pathway (Figure 30.20), the critical control points are the condensation of phosphoenolpyruvate and erythrose-4-phosphate to 3-deoxy-D-arabinoheptulosonate 7-phosphate, DAHP, by DAHP synthase. For tryptophan, the formation of anthranilic acid from chorismic acid by anthranilate synthase is the second critical control point. The transcriptional regulation was overcome through the use of alternative promoters and allosteric regulation was circumvented by the classical technique of selection for feedback-resistant mutants using toxic analogues of the repressing compounds. 

Fig. 13. Left-hand scale Stimulation by 1 mM cyclopenin of in vitro activities of DAHP synthase ( ), chorismate mutase (O), anthranilate synthase (A), and tryptophan synthase ( ). Right-hand scale Cyclopenin content in the culture liquid (0) in 1 cm culture area. From Ref. 67.

Peebles CAM, Hong S-B, Gibson SI, Shanks JV, San K-Y. Transient effects of overexpressing anthranilate synthase a and... 

Figure 6 Proposed biosynthetic pathways from chorismate (37), prephenate (38), and arogenate (41) to Phe (1), Tyr (2), and Trp (43) in plants and microorganisms. ADT, arogenate dehydratase AS, anthranilate synthase CM, chorismate mutase HPPAT, p-hydroxyphenylpyruvate aminotransferase PDH, prephenate dehydrogenase PPAAT, prephenate aminotransferase PPYAT, phenylpyruvate aminotransferase.

Enzymes catalyzing the conversions from chorismate (37), namely, CM and anthranilate synthase (AS) (Figure 6), are also subject to feedback regulation. CM is inhibited by Phe (1) and Tyr (2), and activated by... 

T) anthranilate synthase ( anthranilate phosphoribosyltransferase ( 7V-(5 -phosphoribosyl)-anthranilate isomerase indole-3-glycerol phosphate synthase tryptophan synthase... 

Anthranilate synthase, component I Anthranilate synthase, component II Tryptophan synthase, P subunit Tryptophan synthase, or subunit... 

Anthranilate synthase (I2, II2) iV-(5 -Phosphoribosyl)-anthranilate isomerase Tryptophan synthase ( 2 2) ... 

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