Thiamine diphosphate -dependent

This thermodynamic driving force is particularly useful tvith multienzyme equilibrium systems such as that used in the gram-scale synthesis of tv ro equivalents ofo-xylulose 5-phosphate (104) from (26) (Figure 10.38) [171,172]. Similarly, the corresponding 1-deoxy-D-xylulose 5-phosphate tvas efficiently produced from pyruvate and (34) by the catalytic action of the thiamine diphosphate-dependent 1-deoxy-D-xylulose 5-phosphate synthase (DXS) (EC 2.2.1.7) from E. coli [173]. 

Other thiamine diphosphate-dependent enzymes have recently been scrutinized for their preparative value [166]. Although pyruvate decarboxylase (PDC) (EC 4.1.1.1)... 

Figure 10.40 Stereocomplementary acyloin syntheses based on the carboligation capacity of thiamine diphosphate-dependent enzymes.

Berthold CL, P Moussatche, NGJ Richards, Y Lindqvist (2005) Structural basis for activation of the thiamin diphosphate-dependent enzyme oxalyl-CoA decarboxylase by adenosine diphosphate. J Biol Chem 280 41645-41654. 

Other organisms are equipped to produce ethanol, by employing a thiamine diphosphate-dependent decarboxylation of pyruvate to acetaldehyde (see Section 15.8) and NAD+ is regenerated by reducing the acetaldehyde to ethanol. This is a characteristic of baker s yeast, and forms the essential process for both bread making (production of CO2) and the brewing industry (formation of ethanol). 

The requirement for NAD+ is to reoxidize the lipoic acid carrier. It is worth mentioning that the pyruvate acetaldehyde conversion we considered at the end of the glycolytic pathway involves the same initial sequence, and pyruvate decarboxylase is another thiamine diphosphate-dependent enzyme. 

C-C-Bonding Microbial Enzymes Thiamine Diphosphate-Dependent Enzymes and Class I Aldolases... 

M. S. Hasson, A. Muscate, M. J. McLeish, L. S. Polovnikova, J. A. Gerlt, G. L. Kenyon, G. A. Petsko, D. Ringe, The crystal structure of benzoylformate decarboxylase at 1.6 A resolution, diversity of catalytic residues in thiamin diphosphate-dependent enzymes. Biochemistry 1998, 37, 9918-9930. 

A Thiamine Diphosphate-Dependent Enzymes Multi-purpose Catalysts in Asymmetric Synthesis... 

More recently, enzymatic carboligation in a solid/gas bioreactor was demonstrated to be possible [55] in a model system based on the condensation of two propanal molecules to produce of propioin using thiamine diphosphate-dependent... 

By 1998, X-ray structures had been determined for four thiamin diphosphate-dependent enzymes (1) a bacterial pyruvate oxidase,119120 (2) yeast and bacterial pyruvate decarboxylases,121 122c (3) transketolase,110123124 and (4) benzoylformate decarboxylase.1243 Tire reactions catalyzed by these enzymes are all quite different, as are the sequences of the proteins. However, the thiamin diphosphate is bound in a similar way in all of them. 

Most known thiamin diphosphate-dependent reactions (Table 14-2) can be derived from the five halfreactions, a through e, shown in Fig. 14-3. Each halfreaction is an a cleavage which leads to a thiamin- bound enamine (center, Fig. 14-3) The decarboxylation of an a-oxo acid to an aldehyde is represented by step b followed by a in reverse. The most studied enzyme catalyzing a reaction of this type is yeast pyruvate decarboxylase, an enzyme essential to alcoholic fermentation (Fig. 10-3). There are two 250-kDa isoenzyme forms, one an a4 tetramer and one with an ( P)2 quaternary structure. The isolation of ohydroxyethylthiamin diphosphate from reaction mixtures of this enzyme with pyruvate52 provided important verification of the mechanisms of Eqs. 14-14,14-15. Other decarboxylases produce aldehydes in specialized metabolic pathways indolepyruvate decarboxylase126 in the biosynthesis of the plant hormone indoIe-3-acetate and ben-zoylformate decarboxylase in the mandelate pathway of bacterial metabolism (Chapter 25).1243/127... 

Except for some vitamin B12-dependent reactions, the cleavage or formation of carbon-carbon bonds usually depends upon the participation of carbonyl groups. For this reason, carbonyl groups have a central mechanistic role in biosynthesis. The activation of hydrogen atoms (3 to carbonyl groups permits (3 condensations to occur during biosynthesis. Aldol or Claisen condensations require the participation of two carbonyl compounds. Carbonyl compounds are also essential to thiamin diphosphate-dependent condensations and the aldehyde pyridoxal phosphate is needed for most C-C bond cleavage or formation within amino acids. 

The third type of carbon-branched unit is 2-oxoisovalerate, from which valine is formed by transamination. The starting units are two molecules of pyruvate which combine in a thiamin diphosphate-dependent a condensation with decarboxylation. The resulting a-acetolactate contains a branched chain but is quite unsuitable for formation of an a amino acid. A rearrangement moves the methyl group to the (3 position (Fig. 24-17), and elimination of water from the diol forms the enol of the desired a-oxo acid (Fig. 17-19). The precursor of isoleucine is formed in an analogous way by condensation, with decarboxylation of one molecule of pyruvate with one of 2-oxobutyrate. 

Some bacteria that lack the usual aldolase produce ethanol and lactic acid in a 1 1 molar ratio via the "heterolactic fermentation." Glucose is converted to ribulose 5-phosphate via the pentose phosphate pathway enzymes. A thiamin diphosphate-dependent "phosphoketolase" cleaves xylulose 5-phosphate in the presence of inorganic phosphate to acetyl phosphate and glyceraldehyde 3-phosphate. 

The terpenes, carotenoids, steroids, and many other compounds arise in a direct way from the prenyl group of isopentenyl diphosphate (Fig. 22-1).16a Biosynthesis of this five-carbon branched unit from mevalonate has been discussed previously (Chapter 17, Fig. 17-19) and is briefly recapitulated in Fig. 22-1. Distinct isoenzymes of 3-hydroxy-3-methylglutaryl-CoA synthase (HMG-CoA synthase) in the liver produce HMG-CoA destined for formation of ketone bodies (Eq. 17-5) or mevalonate.7 8 A similar cytosolic enzyme is active in plants which, collectively, make more than 30,000 different isoprenoid compounds.910 However, many of these are formed by an alternative pathway that does not utilize mevalonate but starts with a thiamin diphosphate-dependent condensation of glyceraldehyde 3-phosphate with pyruvate (Figs. 22-1,22-2). 

The pathway also operates in some bacteria and apparently is the sole source of isoprenoid compounds for the unicellular alga Scenedesmus.28 The pathway is outlined in Fig. 22-2. Pyruvate is decarboxylated by a thiamin diphosphate-dependent enzyme,29 and the resulting enamine is condensed with D-glyceraldehyde 3-phosphate to form 1-deoxyxylulose 5-phosphate.28, i0 31a The latter undergoes an isomeroreductase rearrange-... 

As indicated in Fig. 24-17, pyruvate is the starting material for the formation of both l- and D-alanine and also the branched chain amino acids valine, leucine, and isoleucine.339,340 The chemistry of the reactions has been discussed in the sections indicated in the figure. The first step is catalyzed by the thiamin diphosphate-dependent acetohydroxyacid synthase (acetolactate synthase), which joins two molecules of pyruvate or one of pyruvate and one of 2-oxobutyrate (Fig. 24-17 Fig. 14-3).340a b In E. coli there are two isoenzymes encoded by genes ilv B and ilv HI. Both are regulated by feedback inhibition by valine, probably... 

Polled hereford calves in Australia develop maple syrup urine disease relatively often/ 6 One cause was established as a mutation that introduces a stop codon that causes premature termination within the leader peptide during synthesis of the thiamin diphosphate-dependent El subunit. A similar biochemical defect in a mutant of Bacillus subtilis causes difficulties for this bacterium, which requires branched-chain fatty acids in its membranes. Branched acyl-CoA derivatives are needed as starter pieces for their synthesis (Chapter 29). With the oxidative decarboxylation of the necessary oxoacids blocked, the mutant is unable to grow unless supplemented with branched-chain fatty acids. 

Scheme 21. Thiamine-diphosphate-dependent decarboxylation of hydroxypyruvate by transketolase...

Scheme 22. Thiamine-diphosphate-dependent fragmentation of pyruvate by pyruvate decarboxylase...

Results of a kinetic study of enamine formation by C(2a)-proton abstraction from 2-benzylthiazolium salts (88) have implications for mechanistic studies of the thiamin diphosphate-dependent enzymes which feature protonation of the enamine/C(2a)-carbanion.151 The primary isotope effect for deprotonation of (88a) is kiw/kro = 4-6 and the values estimated for C(2a)—H pXa are 15.0-15.5 and 15.7 for (88a) and (88b), respectively. A minimum effective molarity of 4500 M has been estimated for reprotonation of the enamine (89b) derived from (88b) by benzoylformate decarboxylase. Directed aromatic metallation reactions have been reviewed.152... 

Scheme 3 Thiamin diphosphate-dependent decarboxylation of benzoylfonnic acid to benzaldehyde. Reprinted with permission from Reference 50. Copyright 2006 American Chemical Society.

Enantiopure, bifunctional acyloins (a-hydroxy ketones) are versatile intermediates in natural product synthesis (also see Sect. 2.3, Fig. 11). In nature, the formation of a-hydroxy ketones is efficiently catalyzed by thiamine diphosphate-dependent enzymes transketolases, decarboxylases, and other lyases, such as BALs. A great portfolio of biotransformations, especially with benzaldehyde derivatives as starting materials, were realized [204]. 

Muller M, Gocke D et al (2009) Thiamin diphosphate in biological chemistry exploitation of diverse thiamin diphosphate-dependent enzymes for asymmetric chemoenzymatic synthesis. FEBS J 276 2894-2904... 

Pohl M, Lingen B et al (2002) Thiamin-diphosphate-dependent enzymes new aspects of asymmetric C-C bond formation. Chem Eur J 8 5288-5295... 

Possible role of thiamin diphosphate-dependent enzymes in... 

That there is an enamine-like intermediate in all thiamin diphosphate-dependent enzymatic pathways has been suggested for many years, although the issue is still sometimes clouded by the observation that the C2a-protonated form, the C2a-hydro-xyethylThDP when added to oxidases such as pyruvate oxidase (POX) and the pyruvate dehydrogenase multienzyme complex (PDHc), will undergo oxidation. 

Are enamine mimics general transition-state analogs for thiamin diphosphate-dependent enzymes ... 

In a very imaginative piece of research Frost and coworkers have developed a plasmid-based method for synthesizing aromatic amino acids, by incorporating the genes that code for the enzymes that perform the series of conversions from D-fructose-6-phosphate to D-erythrose-4-phosphate to 3-deoxy-D-arabinoheptulosonic acid-7-phos-phate (DAHP) near each other on a plasmid that can be transformed in E. coli. The enzymes are the thiamin diphosphate-dependent enzyme transketolase in the nonoxida-tive pentose shunt and DAHP synthase. The DAHP is then converted to the cyclic dehydroquinate, a precursor to all aromatic amino acids L-Tyr, L-Phe and L-Trp165,166 (equation 27). 

Jordan F (2003) Current mechanistic understanding of thiamine diphosphate-dependent enzymatic reactions. Nat Prod Rep 20 184—201... 

Nilsson U, Meshalkma L, Lindqvist Y, Schneider G (1997) Examination of substrate binding in thiamin diphosphate-dependent transketolase by protein crystallography and site-directed mutagenesis. I Biol Chem 272 1864— 1869... 

The synthetic potential of thiamin diphosphate dependent enzymes is now recognized and has been reviewed recently.84-85 TK has been isolated from... 

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