Transketolasecatalyzed Reaction

Transketolase (TKase) [EC 2.2.1.1] essentially catalyzes the transfer of C-2 unit from D-xylulose-5-phosphate to ribose-5-phosphate to give D-sedoheptulose-7-phosphate, via a thiazolium intermediate as shown in Fig. 16. An important discovery was that hydroxypyruvate works as the donor substrate and the reaction proceeds irreversibly via a loss of carbon dioxide (Fig. 17).31 In this chapter, we put emphasis on the synthesis with hydroxypyruvate, as it is the typical TPP-mediated decarboxylation reaction of a-keto acid.32

The enzyme is available from yeast32'33 and spinach leaves34'35 in quantity. Yeast enzyme is commercially available. TKase gene of many organisms

'-Ribose 5-P D-Sedoheptulose 7-P D-Glyceraldehyde S

Figure 16: Transketolase-catalyzed reaction.

'-Ribose 5-P D-Sedoheptulose 7-P D-Glyceraldehyde S

Figure 16: Transketolase-catalyzed reaction.

Hydroxypyruvate

(e.g., E. colt,36-38 S. cerevisiae39 Spinacia oleracea40 and Rattus norvegicus41) was cloned and overproduced. Moreover, a convenient assay method has been proposed,42 which is very important for the evaluation of enzyme activity from any of these sources.

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