Tryptophan amino transferase

Indoleacetic acid (lAA) (17) is involved in many aspects of plant growth and development (Bonner and Varner, 1976 Kosuge and Sanger, 1986). This hormonal substance is derived in most plants by conversion of tryptophan to indole 3-pyruvic acid (15) (tryptophan amino transferase), decarboxylation to the indole 3-acetaldehyde (16) (indole pyruvate decarboxylase), and oxidation to indole 3-acetic acid (17) (indole acetaldehyde oxidase) (Fig. 7.6) (Goodwin and Mercer, 1983). 

FIGURE 10.19 Deduced amino acid sequence for fructan fructan transferase (FFT) and sucrose sucrose 1-fructosyltransferase (SST). (From van der Meer, I.M. et al., Plant /., 15, 489-500, 1998.) Amino acids in bold represent homology between FFT and SST. Symbols A = alanine C = cysteine D = aspartate E = glutamate F = phenylalanine G = glycine H = histidine I = isoleucine K = lysine L = leucine M = methionine N = asparagine P = proline Q = glutamine R = arginine S = serine T = threonine V = valine W = tryptophan and Y = tyrosine. 

Biosynthesis Like other aromatic amino acids, e.g., Phe and Tyr, Trp is formed on the shikimic acid pathway. There is a branching point at chorismic acid one branch leads to Phe and Tyr, the other to Trp choris-mic acid - anthranilic acid (anthranilic acid synthase, EC 4.1.3.27)- A-(5 -0-phosphoribosyl)-anthranilic acid (anthranilic acid phosphoribosyl transferase, EC 2.4.2.18)- 1 -o-carboxyphenylamino-1 -deoxyribu-lose 5-phosphate [A-(5 -phosphoribosyl)anthranilic acid isomerase]- indole-3-glycerol phosphate (in-dole-3-glycerol phosphate synthase, EC 4.1.1.48) - indole (tryptophan synthase, EC 4.2.1,20)+serine - Trp. Many biologically active indole compounds are derived from Trp, e. g., 5-hydroxytryptophan, 5-hydroxy-tryptamine ( serotonin), and melatonin as well as many indole alkaloids. 

Figure 5.3. Principal metabolic pathways for brain monoamines. AD = aromatic L-amino acid decarboxylase, COMT = catechol-O-methyl-transferase, DH = dopamine-p-hydroxylase, MAO = monoamine oxidase, TH — tyrosine hydroxylase, TPH = tryptophan hydroxylase...

Phosphorylation of 3-hydroxyl group of shikimate by shikimate kinase (EC 2.7.1.71) with ATP as a cosubstrate initiates the biosynthesis pathway of anthranilic acid [2], This step also presents the first step of the shikimate pathway, which is a metabolic route used by bacteria, fungi, and plants for the biosynthesis of many aromatic products such as lignins, alkaloids, flavonoids, benzoic acid, and plant hormones, in addition to the aromatic amino acids (phenylalaiune, tyrosine, and tryptophan). The sequential EPSP synthesis is catalyzed by EPSP synthase (EC 2.5.1.19) through the addition of phosphoenolpyruvate to 3-phospho-shikimate followed elimination of phosphate. EPSP synthase belongs to the family of transferases, specifically to those transferring aryl... 

In the ideal case, methods A, B and C provide equal amounts of (S)- and (i )-a-[ H/ C]-amino acids (or derivatives) upon separation. If complete transformation of racemic material is required, re-racemization of the undesired enantiomer can be accomplished chemically by acid catalysis in the presence of catalytic amounts of salicylaldehyde thermal treatment or enzymatically with the aid of transferases and subjection of the undesired product to repeated resolution cycles, as illustrated for (21 )-[3- C]tryptophan (16). 

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