Amino Acids: 2

Home , Anthranilic acid, Arogenate dehydratase, Chorismate synthase, Flavin mononucleotide, Leucine transaminase, Phosphoenolpyruvic acid

Czech J. Food Sci. Vol. 24, No. 2: 45–58

Biosynthesis of Food Constituents: Amino Acids: 2. The Alanine-Valine-Leucine, Serine-Cysteine-Glycine, and Aromatic and Heterocyclic Amino Acids Groups – a Review

JAN VELÍŠEK and KAREL CEJPEK

Department of Food Chemistry and Analysis, Faculty of Food and Biochemical Technology, Institute of Chemical Technology Prague, Prague, Czech Republic

Abstract

VELÍŠEK J., CEJPEK K. (2006): Biosynthesis of food constituents: Amino acids: 2. The alanine-valine- leucine, serine-cysteine-glycine, and aromatic and heterocyclic amino acids groups – a review. Czech J. Food Sci., 24: 45–58.

This review article gives a survey of principal pathways that lead to the biosynthesis of the proteinogenic amino acids of the alanine-valine-leucine group starting with pyruvic acid from the glycolytic pathway and serine-cysteine-glycine group starting with 3-phospho-D-glyceric acid from the glycolytic pathway. A survey is further given to the aromatic and heterocyclic amino acids (phenylalanine, tyrosine, tryptophan, histidine) starting with 3-phosphoenolpyruvic acid from the glycolytic pathway and D-erythrose 4-phosphate, an intermediate in the pentose phosphate cycle and Calvin cycle.

Keywords: biosynthesis; amino acids; alanine; valine; leucine; serine; glycine; cysteine; phenylalanine; tyrosine; tryptophan; histidine

1 THE ALANINE, VALINE, AND LEUCINE GROUP Alanine is formed from pyruvic acid in a simple transamination reaction (Figure 2) catalysed by 1.1 Alanine alanine transaminase (EC 2.6.1.2) (SENGBUSCH). L-Alanine and the essential amino acids L-valine The transamination reactions are catalysed by and L-leucine have a common precursor, i.e. pyruvic transaminases dependent on the coenzyme pyri- acid from the glycolytic pathway (Figure 1). doxal 5'-phosphate (PLP).

Glycolysis pyruvic acid L-alanine L-glutamic acid 2-oxoglutaric acid

CH3 COOH H3CCOOH L-leucine O EC 2.6.1.2 NH2

pyruvic acid L-alanine L-valine

Figure 1 Figure 2

Partly supported by the Ministry of Education, Youth and Sports of the Czech Republic, Project MSM 6046137305.

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1.2 Valine synthase (EC 2.3.3.13, requires K+ ions), is the condensation of 3-methyl-2-oxobutanoic acid Valine is synthesised in a set of four reactions, with acetyl-CoA to (S)-2-isopropylmalic acid. The and an extension of the valine pathway results in next two steps are catalysed by 3-isopropylmalate leucine synthesis (Figure 3) (IUBMB 2003). The first dehydratase (EC 4.2.1.33). 2-Isopropylmaleic acid three enzymes involved in the biosynthesis of valine arises from 2-isopropylmalic acid by elimination and leucine, i.e. acetolactate synthase (EC 2.2.1.6), of water and addition of water to 2-isopropyl- ketol-acid reductoisomerase (EC 1.1.1.86), and di- maleic acid yields (2R,3S)-3-isopropylmalic acid. hydroxyacid-dehydratase (EC 4.2.1.9), also catalyse The enzyme also hydrates the product back to analogous reactions leading to the biosynthesis (S)-2-isopropylmalic acid, thus bringing about of isoleucine. 3-Methyl-2-oxobutanoic acid is the the interconversion between the two isomers. common precursor of both amino acids, valine and In the next step, 3-isopropylmalic acid is oxi- leucine. This carboxylic acid then yields valine dised to (S)-2-isopropyl-3-oxosuccinic acid by the by the action of the branched-chain-amino-acid NAD+-dependent 3-isopropylmalate dehydroge- transaminase (EC 2.6.1.42). nase (EC 1.1.1.85). The product decarboxylates spontaneously to 4-methyl-2-oxopentanoic acid 1.3 Leucine (4-oxoisocapronic acid), which is, in the last step, transformed to leucine by either branched-chain- Leucine is synthesised from 3-methyl-2-oxobu- amino-acid transaminase (EC 2.6.1.42) or more tanoic acid in six steps (Figure 3) (IUBMB 2003). specific leucine transaminase (EC 2.6.1.6) that The first step, catalysed by 2-isopropylmalate does not act on valine or isoleucine.

CO2 NADPH + H NADP CH CH3 3 COOH H3CCOOH H3C COOH H3C 2 OH OH O EC 2.2.1.6 O EC 1.1.1.86 OH pyruvic acid (S)-2-hydroxy-2-methyl-3-oxobutanoic acid (R)-2,3-dihydroxy-3-methylbutanoic acid

EC 4.2.1.9 H2O

H3C S CoA H2O L-glutamic acid 2-oxoglutaric acid COOH HS CoA + H O COOH O 2 CH3 CH3 H3C COOH H3C COOH COOH COOH H3C H C OH 3 CH3 EC 4.2.1.33 CH O 3 EC 2.3.3.13 EC 2.6.1.42 NH2

2-isopropylmaleic acid (S)-2-isopropylmalic acid 3-methyl-2-oxobutanoic acid L-valine

H2O EC 4.2.1.33

NAD NADH + H CO2 L-glutamic acid 2-oxoglutaric acid COOH COOH H C COOH H3C COOH H3C COOH H3C COOH 3

EC 1.1.1.85 EC 2.6.1.42 CH NH CH3 OH CH3 O CH3 O 3 2 EC 2.6.1.6

(2R,3S)-3-isopropylmalic acid (S)-2-isopropyl-3-oxosuccinic acid 4-methyl-2-oxopentanoic acid L-leucine

Figure 3

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2 THE SERINE, GLYCINE, 2.2 Glycine AND CYSTEINE GROUP The major pathway of glycine biosynthesis is the 2.1 Serine direct transformation of L-serine, which is catalysed by PLP protein, i.e. serine hydroxymethyl trans- L-Serine is generated in a three-step reaction ferase (EC 2.1.2.1). The hydroxymethyl group of the from 3-phospho-D-glyceric acid, formed in the serine side chain is split off and this C1 unit is ac- glycolytic pathway, and becomes the precursor of cepted by tetrahydrofolic acid (H4PteGlu, R = ben- glycine and L-cysteine (Figure 4). zoyl glutamic acid residue) under the formation of 5,10-methylene-tetrahydrofolic acid (5,10-meth- Glycolysis 3-phospho-D-glyceric acid ylene-H4PteGlu) (Figure 6) (SENGBUSCH).

2.3 Cysteine

Cysteine directly or indirectly provides sulfide for structural, regulatory, or catalytic purposes in

glycine L-serine L-cysteine peptides, proteins, and numerous low molecular weight compounds such as methionine, gluta- Figure 4 thione, biotin, and thiamine. Biosynthesis of the cysteine -SH group needs sulfur and thus provides The first step of serine biosynthesis is the oxida- an exclusive entry of reduced sulfur into cellular tion of 3-phospho-D-glyceric acid at C-2 to 3-phos- metabolism. Plants take up sulfur as inorganic phopyruvic acid catalysed by 3-phosphoglycerate sulfate ions. After its uptake by roots, sulfate is dis- dehydrogenase (EC 1.1.1.95). This phosphorylated tributed into different organs and, to be assimilated, oxo-analogue of serine is transaminated by PLP-de- it has to be reduced in a process called assimila- pendent phosphoserine transaminase (EC 2.6.1.52) tory sulfate reduction performed in chloroplasts. in the second step yielding 3-phospho-L-serine. The first step in the sulfate assimilation pathway Finally, in the third step, phosphoserine is hydro- is catalysed by ATP sulfurylase (EC 2.7.7.4). This lysed by phosphoserine phosfatase (EC 3.1.3.3) to enzyme activates sulfate via an ATP-dependent serine (Figure 5) (SENGBUSCH). reaction that leads to the formation of adenylyl-

NAD NADH + H L-glutamic acid 2-oxoglutaric acid H2O P

COOH COOH COOH COOH PO PO PO HO O NH OH EC 1.1.1.95 EC 2.6.1.52 NH2 EC 3.1.3.3 2

3-phospho-D-glyceric acid 3-phosphopyruvic acid 3-phospho-L-serine L-serine

Figure 5

10 R R OH H N OH N H N N COOH N 5 COOH N HO + + + H2O NH NH H N N N 2 H2N N N EC 2.1.2.1 2 2 H H

L-serine H4PteGlu glycine 5,10-methylene-H4PteGlu

Figure 6

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NH2 NH2

N N N N OH OH 2 GSH G-S-S-G OH O S OPO CH N N CH 2 O OH HO PO 2 O N N O O OS + O OH EC 1.8.4.9 OH OH OH OH adenosine-5´-phosphosulfate sulfurous acid adenosine-5´-phosphate

ATP

EC 2.7.1.25 SH HS S S O O H H N N ADP NH R R R 2 R NH2 O O N N N N OH OH thioredoxin (reduced) thioredoxin (oxidized) OH

O S OPO CH2 N N HO O OH PO CH2 O N N O O OS + O OH EC 1.8.4.8 O OH O OH O P OH O P OH OH OH adenosine-5´-phosphosulfate-3´-phosphate sulfurous acid adenosine-3´,5´-diphosphate

Figure 7 sulfate (adenosine-5'-phosphosulfuric acid, APS) and plants. Sulfite is reduced to sulphide at the and inorganic diphosforic acid (PP). expense of oxidising three molecules of NADPH, To accomplish the incorporation of sulphur into by sulphite reductase (EC 1.8.7.1)1. biomolecules, specifically amino acids, sulphate Depending on the organism, there are two dif- in APS is transformed into sulphite and this into ferent ways by which sulfide is incorporated into a sulphide. This process may occur through two carbon backbone to produce L-cysteine (Figure 8). different pathways, depending on the organism. First, the physiological O-ester substrate O-ace- One of them involves phosforylation of APS by tylserine is synthesised from L-serine by serine adenosine 5'-phosphosulfate kinase (EC 2.7.1.25) acetyltransferase (EC 2.3.1.30). Sulfide is condensed using ATP to produce 3'-phosfoadenosine-5'-phos- with O-acetylserine by the PLP-dependent enzyme phosulfate (PAPS) and ADP. In the following re- O-acetylserine (thiol)-lyase (also called O-acetyl- action, PAPS reductase (EC 1.8.4.8) firstly reacts serine sulfhydrylase, EC 2.5.1.47) to form cysteine with reduced thioredoxin and then with PAPS to directly. Because the substrate O-acetylserine is generate free sulphite. The other pathway involves derived from the carbon and nitrogen assimilatory the direct reduction of APS by 5'-adenylylsulfate pathways, the O-acetylserine (thiol)-lyase links reductase (EC 1.8.4.9), which uses GSH as an the sulfur and nitrogen assimilatory pathways electron source to produce sulphite. In yeasts and together. many bacteria, sulphite is synthesised via adeno- O-acetylserine sulphhydrylase (EC 2.5.1.47) also sine 5'-phosphosulfate kinase, whereas in plants, catalyses the condensation of sulfide with O-acetyl- green algae, and phototrophic bacteria, sulfate is homoserine to form L-homocysteine. O-Acetyl- transformed into sulphite via 5'-adenylylsulfate homoserine is synthesised from L-homoserine reductase (Figure 7). by homoserine O-acetyltransferase (EC 2.3.1.31). Once sulfate has been reduced to sulphite, the Then homocysteine is transformed into cysteine subsequent step is identical in bacteria, fungi, by trans-sulfuration, i.e. L-homocysteine asso-

1Sulphite reductase contains a special acidic heme group called siroheme and catalyses the reduction of sulfite using electrons donated by ferredoxin.

48 Czech J. Food Sci. Vol. 24, No. 2: 45–58

acetyl-CoA HS-CoA O H2S CH3 COOH COOH COOH COOH HO H3C O HS NH NH NH 2 EC 2.3.1.30 2 EC 2.5.1.47 2 L-serine O-acetyl-L-serine L-cysteine

Figure 8

acetyl-CoA HS-CoA H2SCH3 COOH

HO COOH H3CO COOH HS COOH

O NH NH NH2 EC 2..3.1.31 2 EC 2.5.1.47 2 L-homoserine O-acetyl-L-homoserine L-homocysteine

COOH L-serine H3C + NH3 O EC 4.2.1.22 2-oxobutyric acid H2O NH2 COOH S COOH HS HOOC

NH2 EC 4.4.1.1 NH2

L-cysteine L,L-cystathionine

Figure 9 ciates with serine to form L,L-cystathionine by route to the aromatic amino acids L-phenylalanine action of cystathionine β-synthase (EC 4.3.1.22). and L-tyrosine and to the heterocyclic amino acid Cystathionine in turn dissociates into cysteine, L-tryptophan (IUBMB 2001). Shikimic acid2, a 2-oxobutyric acid, and ammonia by cystathionine central intermediate in this pathway, is formed γ-lyase (EC 4.4.1.1) (Figure 9) (JOST et al. 2000). by a sequence of reactions from 3-phospho- Cysteine may also be transformed into homo- enolpyruvic acid (from glycolysis) and D-eryth- cysteine by reverse trans-sulphuration catalysed rose 4-phosphate (from the pentose phosphate by cystathionine γ-synthase (EC 2.5.1.48) and cycle and the Calvin cycle). Both shikimic acid cystathionine β-lyase (EC 4.4.1.8). and the subsequent chorismic acid are important The serine acetyltransferase pathway is used by intermediates. The latter is the starting compound plants and by enteric bacteria. Fungi use different for three different pathways that lead to the end cysteine biosynthetic pathway depending on the products phenylalanine, tyrosine, and tryptophan. species. In plants, cysteine can also be produced An activated form of D-ribose 5-phosphate by the degradation of methionine. (5-phospho-α-D-ribose 1-diphosphate), is an- other intermediate of tryptophan biosynthesis. 3 THE AROMATIC AND HETEROCYCLIC It has also a key position in the biosynthesis of AMINO ACIDS GROUP L-histidine. The biosynthetic pathway of histidine is unusual in that histidine is produced from a 3.1 Phenylalanine and tyrosine purine. Animals employ none of these pathways Biosynthetic pathways of the aromatic and het- and, accordingly, these amino acids feature among erocyclic amino acids family is schematically shown those essential amino acids for man that have to in Figure 10. The shikimic acid pathway provides a be obtained in the diet.

2Shikimic acid has been isolated from plants of Illicium anisatum L., syn. I. religiosum Sieb. et Zucc., Japanese shikimi.

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Glycolysis Pentose phosphate cycle

3-phosphoenolpyruvic acid D-erythrose 4-phosphate D-ribose 5-phosphate Photosynthesis

5-phospho-D-ribose 1-diphosphate

shikimic acid

L-histidine

chorismic acid L-tryptophan

prephenic acid

L-phenylalanine L-tyrosine

Figure 10

The shikimic acid pathway begins with an aldol- kimate dehydrogenase (EC 1.1.1.282) yields quinic type condensation of phosphoenolpyruvic acid with acid, a fairly common acid frequently occurring D-erythrose 4-phosphate to give the seven-carbon in foods in the free and esterified form3. 3-Dehy- 3-deoxy-D-arabino-heptulosonic acid 7-phosphate droshikimic acid is formed from 3-dehydroquinic (3-deoxy-7-phospho-D-arabino-heptulosonic acid, acid by dehydration catalysed by 3-dehydroquin- Figure 11). This reaction catalysed by 3-deoxy- ate dehydratase (EC 4.2.1.10) (Figure 14) (IUBMB 7-phosphoheptulonate synthase (EC 2.5.1.54) is 2001). Reduction of 3-dehydroshikimic acid by mechanistically a complex reaction (Figure 12) NADP+-dependent shikimate 3-dehydrogenase (IUBMB 2002). Elimination of phosphoric acid (EC 1.1.1.25) or quinate/shikimate dehydrogenase from 3-deoxy-7-phospho-D-arabino-heptulosonic (EC 1.1.1.282) yields shikimic acid. This second acid followed by intramolecular aldol reaction shikimate dehydrogenase enzyme differs from generates the first alicyclic intermediate 3-dehyd- shikimate 3-dehydrogenase (EC 1.1.1.25) in that roquinic acid. The elimination of phosphoric acid it can use both quinate and shikimate as substrate by 3-dehydroquinate synthase (EC 4.2.3.4) actually and either NAD+ or NADP+ as acceptor. follows a NAD+-dependent oxidation (NAD+ is An important branch point compound in the bound as a prosthetic group) of the central sec- shikimate pathway is chorismic acid. Chorismic ondary hydroxyl group, which is then re-formed acid forms from shikimic acid, which is first phos- in a NADH-dependent reduction reaction on the phorylated by shikimate kinase (EC 2.7.1.71) and intermediate carbonyl compound prior to the aldol yields 3-phosphoshikimic acid. 3-Phosphoshikimic reaction occurring (Figure 13) (BENDER et al. 1989; acid reacts, under catalysis of 3-phosphoshikimate GOURLEY et al. 1999; IUBMB 2001). 1-carboxyvinyltransferase (EC 2.5.1.19), with fur- Reduction of 3-dehydroquinic acid with either ther molecule of phosphoenolpyruvic acid, which quinate dehydrogenase (EC 1.1.1.24) or quinate/shi- is incorporated as an enol ether side-chain in

3Reduction of 3-dehydroquinic acid in bacteria can be achieved also by a quinoprotein, NAD(P)-independent quinate- dehydrogenase (pyrroloquinoline-quinone) (EC 1.1.99.25).

50 10 Czech J. Food Sci. Vol. 24, No. 2: 45–58

H2CCOOH

+ H2O OP COOH phosphoenolpyruvic acid P O P NADPH + H NADP

CH=O CH2 HOCOOH HOCOOH HOH HOH HOH EC 2.5.1.54 HOH EC 4.2.3.4 O OH EC 1.1.1.24 HO OH CH2OP HOH OH EC 1.1.1.282 OH CH2OP D-erythrose 4-phosphate 3-deoxy-7-phospho-D-arabino- 3-dehydroquinic acid quinic acid heptulosonic acid

EC 4.2.1.10 H2O

COOH ADP ATP COOH NADP NADPH + H COOH

PO OH EC 2.7.1.71 HO OH EC 1.1.1.25 O OH OH OH EC 1.1.1.282 OH 3-phosphoshikimic acid shikimic acid 3-dehydroshikimic acid

H2CCOOH

OP EC 2.5.1.19 phosphoenolpyruvic acid

P P COOH COOH

CH2 CH2

PO O COOH EC 4.2.3.5 O COOH OH OH

5-(1-carboxyvinyl)-3-phosphoshikimic acid chorismic acid

Figure 11

P O O H2O O enzyme H enzyme O enzyme O O

H2CCOOH CH2 COOH H H2C COOH O P H OP phosphoenolpyruvic acid COOH CH=O O HOH

CH2 HOH HOH CH2OP HOH D-erythrose 4-phosphate HOH

CH2OP

3-deoxy-7-phospho-D-arabino-heptulosonic acid

Figure 12

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COOH NAD NADH + H O H OH OH O CH2 OH OP HOH HOOC O HOOC O HOH O P OH OH H HOH B CH2OP 3-deoxy-7-phospho-D-arabino-heptulosonic acid

P NAD NADH + H H O OH OH OH O OH O HOOC O HOOC HOOC O P O CH CH2 O 2 OH OH H

H H HO COOH OH OH OH OH HOOC O HOOC H C O OH O CH2 O 2 O OH H 3-dehydroquinic acid

Figure 13

5-(1-carboxyvinyl)-3-phosphoshikimic acid (Fig- The biologically unique conversion of choris- ure 15). The transformation of 5-(1-carboxyvinyl)- mic acid to prephenic acid by chorismate mutase 3-phosphoshikimic acid to chorismic acid involves (EC 5.4.99.5) is formally a Claisen rearrangement a 1,4-elimination of phosphoric acid by chorismate reaction (Figures 17 and 18). Decarboxylation synthase (EC 4.2.3.5) (Figure 16) (FLOSS et al. and loss of hydroxyl group from prephenic acid 1972; BORNEMANN et al. 1996, 2000; JAKEMAN et (prephenate dehydratase, EC 4.2.1.51) yields phe- al. 1998; LEWIS et al. 1999; OSBORNE et al. 2000; nylpyruvic acid, and the PLP-dependent transami- IUBMB 2001). nation catalysed by aromatic aminotransferase

BH H2O HO COOH B HO COOH HO COOH H

enzyme enzyme enzyme NH2 O OH N OH N OH H OH OH H OH 3-dehydroquinic acid

H2O

COOH H2O COOH

O OH enzyme N OH OH OH 3-dehydroshikimic acid

Figure 14

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COOH COOH B P COOH H H CH2 CH2 H2CCOOH COOH PO OH PO O PO O COOH OP O P OH OH OH phosphoenolpyruvic acid 3-phosphoshikimic acid 5-(1-carboxyvinyl)-3-phosphoshikimic acid

Figure 15

COOH FMNH2 FMNH + P COOH FMNH + P FMNH2 + H COOH

COOH COOH COOH

PO O CH2 O CH2 O CH2 OH OH OH 5-(1-carboxyvinyl)-3-phosphoshikimic acid chorismic acid

Figure 16

(EC 2.6.1.57) forms phenylalanine. In the presence (EC 1.3.1.13) decarboxylation occurs with reten- of a NAD+-dependent dehydrogenase (prephen- tion of the hydroxyl function. Transamination ate dehydrogenase, EC 1.3.1.12), or a NADP+- of the resultant 4-hydroxyphenylpyruvic acid by dependent prephenate dehydrogenase (NADP+) aromatic-amino-acid transaminase (EC 2.6.1.57)

L-glutamic acid 2-oxoglutaric acid COOH COOH

O EC 2.6.1.57 NH2

phenylpyruvic acid L-phenylalanine

+ H2O CO2 H2O + CO2

EC 4.2.1.51 EC 4.2.1.91

H H O L-glutamic acid 2-oxoglutaric acid COOH COOH COOH H HOOC O O NH2 CH2

O COOH EC 5.4.99.5 EC 2.6.1.57 OH OH OH

chorismic acid prephenic acid L-arogenic acid

NAD(P) NAD EC 1.3.1.12 EC 1.3.1.43 EC 1.3.1.13 NAD(P)H + H + CO2 NADH + H + CO2 L-glutamic acid 2-oxoglutaric acid COOH COOH

O NH2 HO HO EC 2.6.1.57 EC 2.6.1.5 4-hydroxyphenylpyruvic acid L-tyrosine

Figure 17

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CH2 HOOC COOH HOOC HOOC O COOH O COOH O O O CH2 COOH H O O OH OH H O H chorismic acid conformers prephenic acid

pseudo-diaxial pseudo-diequatorial

Figure 18 or tyrosine transaminase (EC 2.6.1.5) subsequently is reduced to water (Figure 19). The rationalised gives tyrosine (CLARK et al. 1990; IUBMB 2001; reaction mechanism is given in Figure 20 (CARR MARTÍ et al. 2003). et al. 1995; IUBMB 2001). L-Arogenic acid is the result of transamination of prephenic acid occurring prior to the decar- 3.2 Tryptophan boxylation, and can be transformed into both phenylalanine and tyrosine depending on the Tryptophan is derived from chorismic acid via absence or presence of a suitable enzyme activity, anthranilic (2-aminobenzoic) acid in a reaction e.g. activity of arogenate dehydratase (EC 4.2.1.91) catalysed by anthranilate synthase (EC 4.1.3.27) and arogenate dehydrogenase (EC 1.3.1.43), re- (Figure 21). In some organisms this enzyme is a spectively (IUBMB 2003). In animals, which part of a multifunctional protein having more other lack this pathway, direct hydroxylation of phe- enzymatic activities for the biosynthesis of tryp- nylalanine to tyrosine (and of tyrosine to DOPA) tophan, i.e. anthranilate phosphoribosyltransferase may be achieved. This reaction is catalysed by (EC 2.4.2.18), phosphoribosylanthranilate isomer- (6R)-5,6,7,8-tetrahydro-L-biopterin (L-erythro- ase (EC 5.3.1.24), indole-3-glycerol-phosphate

5,6,7,8-tetrahydrobiopterin, BH4)-dependent hy- synthase (EC 4.1.1.48), and tryptophan synthase droxylase enzyme (phenylalanine hydroxylase, (EC 4.2.1.20) activity (IUBMB 2001). EC 1.14.16.1)4, the hydroxyl oxygen being derived Chorismic acid is first aminated at C-2 by L-glu- from molecular oxygen. The second oxygen atom tamine to give 2-amino-2-deoxyisochorismic acid,

O2 H2O OH O OH O H 4a COOH H3C N COOH H3C N N 5 4 NH + 6 3 + 2 NH OH NH OH 7 8 1 EC 1.14.16.1 HO 2 2 N NNH2 N 8a NNH2 H H L-tyrosine 7,8-dihydrobiopterin L-phenylalanine 5,6,7,8-tetrahydrobiopterin

Figure 19

COOH COOH COOH COOH

H NH H NH2 2 NH2 NH2 H O HO O H HH L-phenylalanine L-tyrosine

Figure 20

4The product of tetrahydrobiopterin reduction is 4a-hydroxytetrahydrobiopterin. It can dehydrate 6,7-dihydrobiopterin, both spontaneously and by the action of 4a-hydroxytetrahydropterin dehydratase (EC 4.2.1.96). The 6,7-dihydrobiopterin can be enzymatically reduced back to tetrahydrobiopterin by 6,7-dihydropteridine reductase (EC 1.5.1.34), or spontaneously rearranges to the more stable 7,8-dihydrobiopterin.

54 Czech J. Food Sci. Vol. 24, No. 2: 45–58

H3CCOOH � P O CH2 O 5-phospho- -D-ribose 1-diphosphate O HOOC pyruvic acid O PP COOH Gln Glu COOH OHOH PP P O CH2 O H N NH2 CH2

OCOOH EC 4.1.3.27 EC 2.4.2.18 OHOH OH

chorismic acid anthranilic acid N-(5-phospho-�-D-ribosyl)anthranilic acid

EC 5.3.1.24 CHO HOH D-glyceraldehyde 3-phosphate H2O+ CO 2 COOH CH2OP Ser OH COOH OP NH HO NH2 OH OP N EC 4.2.1.20 N EC 4.1.1.48 H H OOH

L-tryptophan (1S,2R)-1-(indol-3-yl)glycerol 3-phosphate 1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate

Figure 21 which yields anthranilic acid by elimination of 5-Phospho-α-D-ribose 1-diphosphate is the ac- the C-4 hydroxyl as water and C-3 substituent as tivated form of ribose. It forms from either AMP pyruvic acid (Figure 22). The transformation in- in a reaction catalysed by adeninephosphoribosyl volves an SN2'-type of reaction, incoming ammonia, transferase (EC 2.4.2.7) or from D-ribose 5-phos- generated from glutamine, acts as a nucleophile phate (forming in pentose phosphate pathway) attacking the diene system. and ATP by ribose-phosphate diphosphokinase

H2CCOOH H3CCOOH

O HOOC COOH O H O pyruvic acid COOH COOH NH COOH H2N 2 COOH NH2 NH2 NH2 CH2 CH H 2 OCOOH O COOH OH

chorismic acid 2-amino-2-deoxyisochorismic acid anthranilic acid

Figure 22

PP adenine AMP ATP PO O PO O OH AMP OPP EC 2.4.2.7 EC 2.7.6.1 OHOH OHOH o

5-phospho-�-D-ribose 1-diphosphate D-ribose 5-phosphate

Figure 23

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CH O HOH

CH2OP D-glyceraldehyde 3-phosphate H OH O

H2C COOH OP OP OH OH N N H N N H H H HO OP (1S,2R)-1-(indol-3-yl)glycerol 3-phosphate indole H H3C N H H COOH COOH

N N NH N H H2O HO HO OP OP

H3C N H3C N H Schiff base

COOH H2O HO COOH HO NH2 HO N L-serine H2O COOH HO HO OP OP

NH2 N H3C N H3C N H

L-tryptophan pyridoxal 5´-phosphate Schiff base

Figure 24

(EC 2.7.6.1) (Figure 23). It has also a key posi- The early stages of histidine biosynthesis involve tion in the biosynthesis of histidine and purine condensation of 5-phospho-α-D-ribose 1-di- nucleotides (IUBMB 2003). phosphate with ATP, followed by elimination of The tryptophan synthase multienzyme complex diphosphoric acid, which is catalysed by ATP (EC 4.2.1.20) catalyses the final step of tryp- phosphoribosyltransferase (EC 2.4.2.17). Elimi- tophan biosynthesis in its two subunits. In the first nation of diphosphoric acid from this product, enzyme subunit, (1S,2R)-1-(indol-3-yl)glycerol N1-5'-phosphoribosyl-ATP, is catalysed by phos- 3-phosphate splits off D-glyceraldehyde 3-phosphoribosyl-ATP diphosphatase (EC 3.6.1.31) and phate and yields indole. Indole moves to the sec- yields N'-5'-phosphoribosyl-AMP. The pyrimidine ond enzyme subunit where it reacts with the ring of this compound opens by phosphoribo- dehydrated Schiff base of L-serine yielding the syl-AMP cyclohydrolase (EC 3.5.4.19) under the tryptophan-PLP Schiff base, which is then hy- formation of N'-5'-phosphoribosylformimino-5-ami- drolysed to the parent compounds, tryptophan no-imidazole-4-carboxamide ribonucleotide. and PLP (Figure 24). Then 1-(5-phosphoribosyl)-5-[(phosphoribosyl amino)methylene amino]imidazole-4-carboxa- 3.3 Histidine mide isomerase (EC 5.3.1.16) splits the ribose attached at N1 to form 5-amino-4-carboxamide The biosynthetic pathway of L-histidine is unu- ribonucleotide and the intermediate fragment, sual in that five of its carbon atoms are produced which reacts with ammonia from glutamine to from 5-phospho-α-D-ribose 1-diphosphate, the form 3-(imidazol-4-yl)-1-glycerol phosphate. The key intermediate of tryptophan biosynthesis. reaction catalysed by imidazoleglycerol-phosphate One carbon atom comes from ATP (Figure 25). dehydratase (EC 4.2.1.19) converts this compound

56 Czech J. Food Sci. Vol. 24, No. 2: 45–58

H NH NH NH

PO O N N PO O N N PO O N N

OPP N N N N N N PP H O PP OH OH OH OH 2 OH OH PPPO CH2 O PPPO CH2 O PO CH2 O 5-phospho-�-D-ribose 1-diphosphate EC 2.4.2.17 EC 3.6.1.31 OH OH OH OH OH OH

ATP NH2

O N EC 3.5.4.19 H2O

H2N N

PO CH2 NH O NH2 2

O N O N H H PO O PO OH N N OH OH N N N N H H N PO OH PO CH O PO CH2 2 OH O O OHOH O

EC 5.3.1.16 OH O Gln OH OH OH OH

Glu

OH H

OP OP OP N N N NH OH NH O NH OH EC 4.2.1.19 3-(imidazol-1-yl)-2-oxopropylphosphate L-glutamic acid

EC 2.6.1.9

2 NAD 2 NADH + H 2-oxoglutaric acid P H2O COOH OH OP N N N NH NH2 NH NH2 NH NH EC 1.1.1.23 EC 3.1.3.15 2

L-histidine L-histidinol L-histidinol phosphate

Figure 25 to 3-(imidazol-4-yl)-2-oxopropyl phosphate, which EC (Enzyme Commission) numbers and some yields, in a transamination reaction catalysed by common abbreviations a PLP protein histidinol-phosphate transaminase (EC 2.6.1.9), L-histidinol phosphate. Histidinol EC (Enzyme Commission) numbers, assigned by phosphate is hydrolysed to L-histidinol by his- IUPAC-IUBMB, were taken from KEGG: Kyoto Ency- tidinol-phosphatase (EC 3.1.3.15) and histidinol clopedia of Genes and Genomes, http://www.biologie. is finally oxidised to L-histidine by the NAD-de- uni-hamburg.de. In many structures, the abbreviation pendent histidinol dehydrogenase (EC 1.1.1.23) P is used to represent the phosphate group and PP (IUBMB 2001). the diphosphate group. At physiological pH, these

57 Vol. 24, No. 2: 45–58 Czech J. Food Sci. and some other groups will be ionized, but in pictures 7-phosphate synthetase reaction and the chorismate the unionised forms are depicted to simplify the synthetase reaction. Journal of Biological Chemistry, structures, to eliminate the need for counter-ions, 247: 736–744. and to avoid the mechanistic confusion. GOURLEY D.G., SHRIVE A.K., POLIKARPOV I., KRELL T., COGGINS J.R., HAWKINS A.R., ISAACS N.W., SAWYER ADP – denosine 5'-diphosphate L. (1999): The two types of 3-dehydroquinase have dis- AMP – adenosine 5'-monophosphate tinct structures but catalyze the same overall reaction. APS – adenosine-5'-phosphosulfuric acid Nature Structural Biology, 6: 521–525. ATP – adenosine 5'-triphosphate IUBMB (2001): http://www.chem.qmul.ac.uk/iubmb/en- CoA – coenzyme A as a part of a thioester zyme/reaction/. FMN – flavin mononucleotide IUBMB (2002): http://www.chem.qmul.ac.uk/iubmb/en- GSH – glutathione (reduced) zyme/reaction/. GSSG – glutathione (oxidised) IUBMB (2003): http://www.chem.qmul.ac.uk/iubmb/en- NADH – nicotinamide adenine dinucleotide zyme/reaction/. NADPH – nicotinamide adenine dinucleotide phos- JAKEMAN D.L., MITCHELL D.J., SHUTTLEWORTH W.A., phate EVANS J.N. (1998): On the mechanism of 5-enolpyru- P – phosphoric acid vylshikimate-3-phosphate synthase. Biochemistry, 37: PAPS – 3'-phosphoadenosine-5'-phosphosulfate 12012–12019. PLP – pyridoxal 5'-phosphate JOST R., BERKOWITZ O., WIRTZ M., HOPKINS L., HAWKES- PP – diphosphoric acid FORD M.J., HELL R. (2000): Genomic and functio- nal characterization of the oas gene family encoding Reference s O-acetylserine(thiol)lyases, enzymes catalyzing the final step in cysteine biosynthesis in Arabidopsis thaliana. BENDER S.L., MEHDI S., KNOWLES J.R. (1989): Dihyd- Gene, 253: 237–247. roquinate synthase: the role of divalent metal cations LEWIS J., JOHNSON K.A., ANDERSON K.S. (1999): The and of nicotinamide adenine dinucleotide in catalysis. catalytic mechanism of EPSP synthase revised. Bio- Biochemistry, 28: 7555–7560. chemistry, 38: 7372–7379. BORNEMANN S., LOWE D., THORNELEY R.N. (1996): MARTÍ S., ANDRÉS J., MOLINER V., SILLA E., TUŇÓN I., The transient kinetics of Escherichia coli chorismate BERTRÁN J. (2003): Conformational equilibrium of synthase: substrate consumption, product formation, chorismate. A QM/MM theoretical study combining phosphate dissociation, and characterization of a flavin statistical simulations and geometry optimistations in intermediate. Biochemistry, 35: 9907–9916. gas phase and in aqueous solution. Journal of Molecular BORNEMANN S., THEOCLITOU M.E., BRUNE M., WEBB Structure (Theochem), 632: 197–206. M.R., THORNELEY R.N., ABELL C.A. (2000): A secondary OSBORNE A., THORNELEY R.N., ABELL C., BORNEMANN β deuterium kinetic isotope effect in the chorismate syn- S. (2000): Studies with substrate and cofactor analo- thase reaction. Bioorganic Chemistry, 28: 191–204. gues provide evidence for a radical mechanism in the CARR R.T., BALASUBRAMANIAN S., HAWKINS P.C., BEN- chorismate synthase reaction. Journal of Biological KOVIC S.J. (1995): Mechanism of metal independent Chemistry, 275: 35825–35830. hydroxylation by Chromobacterium violaceum phenyl- SENGBUSCH P.: Botany Online – The Internet Hypertext- alanine hydroxylase. Biochemistry, 34: 7525–7532. book. http://biologie.uni-hamburg.de/b_online/e00/ CLARK T., STEWART J.D., GANEM B. (1990): Transiti- default.htm. on-state analogue inhibitors of chorismate mutase. Received for publication June 13, 2005 Tetrahedron, 46: 731–748. FLOSS H.G., ONDERKA D.K., CARROLL M. (1972): Stereo- Accepted after corrections September 26, 2005 chemistry of the 3-deoxy-D-arabino-heptulosonate

Corresponding author: Prof. Ing. JAN VELÍŠEK, DrSc., Vysoká škola chemicko-technologická v Praze, Fakulta potravinářské a biochemické technologie, Ústav chemie a analýzy potravin, Technická 5, 166 28 Praha 6, Česká republika tel.: + 420 220 443 177, fax: + 420 233 339 990, e-mail: [email protected]