Using thiamin diphosphate

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... 

The conversion of pyruvate (CH3COCO2 ) to ethanol (CH3CH2OH) requires two steps. First, the pyruvate undergoes decarboxylation with participation of the enzyme pyruvate decarboxylase (EC 4.1.1.1). The enzyme uses thiamine diphosphate as a cofactor. As was the case earlier (Scheme 11.7), the nucleophilic ylid adds to the carbon of the carbonyl. In this case, the addition product corresponds to a p,y-unsaturated carboxylic acid, ready for decarboxylation to produce an enol. Protonation followed by elimination of the thiamine diphosphate ylid then yields ethanal (acetaldehyde, CH3CHO).This process is shown in Scheme 11.28. 

Pyruvate dehydrogenase complex. Allen et al.(1964) and later de Vries et al.(1973) postulated that this complex in P. shermanii includes pyruvate dehydrogenase that uses thiamine diphosphate as coenzyme, dihydrolipoyl transacetylase containing lipoic acid, and dihydrolipoyl dehydrogenase containing NAD and FAD. The complex catalyzes the following reaction ... 

The enzyme is a transketolase and the process is called transketolation (keto-carrying). Transketolase uses thiamin diphosphate as a coenzyme to bring about the transfer of a 2-carbon unit from one sugar (a 2-keto sugar) to aldoses (monosaccharides with the characteristic aldehyde group [-CHO]). 

More advanced organisms, like yeasts, can use thiamine diphosphate with different enzymes to oxidize glucose to ethanol and carbon dioxide (Figure 2.13). The NADH produced in the glucose break-down is then used to reduce acetaldehyde to ethanol. Yeast is therefore used by the brewer for the alcohol produced and by the baker for the CO2 to aerate the bread. 

CARBON-CARBON BOND FORMATION USING THIAMIN DIPHOSPHATE (THDP)-DEPENDENT CARBOLIGASES... 

Aldehydes and ketones are converted into alkenes by means of a nucleophilic addition called the Wittig reaction. The reaction has no direct biological counterpart but is important both because of its wide use in the laboratory and drug manufacture and because of its mechanistic similarity to reactions of the coenzyme thiamin diphosphate, which well see in Section 29.6. 

Stepl of Figure 29.11 Addition of Thiamin Diphosphate The conversion of pyruvate to acetyl CoA begins by reaction of pyruvate with thiamin diphosphate, a derivative of vitamin B(. Formerly called thiamin pyrophosphate, thiamin diphosphate is usually abbreviated as TPP. The spelling thiamine is also correct and frequently used. 

Thiamine is present in cells as the free form 1, as the diphosphate 2, and as the diphosphate of the hydroxyethyl derivative 3 (Scheme 1) in variable ratio. The component heterocyclic moieties, 4-amino-5-hydroxymethyl-2-methylpyrimidine (4) and 4-methyl-5-(2-hydroxyethyl)thiazole (5) are also presented in Scheme 1, with the atom numbering. This numbering follows the rules of nomenclature of heterocyclic compounds for the ring atoms, and is arbitrary for the substituents. To avoid the use of acronyms, compound 5 is termed as the thiazole of thiamine or more simply the thiazole. This does not raise any ambiguity because unsubstituted thiazole is encountered in this chapter. Other thiazoles are named after the rules of heterocyclic nomenclature. Pyrimidine 4 is called pyramine, a well established name in the field. A detailed account of the present status of knowledge on the biosynthesis of thiamine diphosphate from its heterocyclic moieties can be found in a review by the authors.1 This report provides only the minimal information necessary for understanding the main part of this chapter (Scheme 2). 

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]. 

For this type of C-C bond formation both stereoisomers of the hydroxyphenyl-propanone can be obtained using either the BFD mentioned above or the benz-aldehyde lyase (BAL). Both of these enzymes are dependent on thiamine diphosphate (ThDP) as cofactor [22]. For the enantioselective reduction of the intermediate also, both stereoisomers can be obtained by using two different ADH enzymes. Thus all four possible stereoisomers of the diol can be obtained in high optical purity (see Scheme. 3.1.1) [23]. 

A small amount of thiamin is excreted in the urine unchanged, accounting for about 3% of a test dose, together with small amounts of thiamin monophosphate and thiamin diphosphate. As discussed in Section 6.5.1, this can be used to assess thiamin nutritional status. One of the major excretory products is thiochrome cyclization to thiochrome is the basis of the normal method of determining thiamin so, most reports of thiamin excretion are actually of thiamin plus thiochrome. In addition, small amounts of thiamin disulfide, formed by the oxidation of thiamin thiol, are also excreted. 

Activation of apotransketolase in erythrocyte lysate by thiamin diphosphate added in vitro has become the most widely used and accepted index of thiamin nutritional status. Apotransketolase is unstable both in vivo and in vitro therefore, problems may arise in the interpretation of results, especially if samples have been stored for any appreciable time. An activation coefficient >1. 25 is... 

Pyruvate oxidase (Pyox) is a FAD- and thiamine diphosphate (ThDP)-dependent enzyme that catalyzes the reaction of pyruvate to give acetyl phosphate or vice versa (see Fig. 15). If used in the oxidative way, it can be activated and reactivated under nonaerobic conditions using ferrocene mediators. Kinetic parameters of the indirect electrochemical process using the enzyme incorporated into a biomimetic supported bilayer at a gold electrode have been reported [142]. Similarly, FAD-dependent amino oxidases may also be applied. 

The coenzyme thiamin diphosphate (ThDP, I in Scheme 16.1), the biologically active form of vitamin Bi, is used by different enzymes that perform a vide range of catalytic functions, such as the oxidative and nonoxidative decarboxylation of a-ketoacids, the formation of acetohydroxyacids and ketol transfer bet veen sugars. 

Schutz, a., Golbik, R., Konig, S., Hubner, G., Tittmann, K. (2005), Intermediate and transition states in thiamin diphosphate-dependent decarboxylases. A kinetic and NMR study on wild-type indolepyruvate decarboxylase and variants using indolepyruvate, benzoylformate, and pyruvate as substrates. Biochemistry 44, 6164-6179. 

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