Microbial transketolase

Like transketolase, transaldolase (TA, E.C. 2.2.1.2) is an enzyme in the oxidative pentose phosphate pathway. TA is a class one lyase that operates through a Schiff-base intermediate and catalyzes the transfer of the C(l)-C(3) aldol unit from D-sedoheptulose 7-phosphate to glyceraldehyde-3-phosphate (G3P) to produce D-Fru 6-P and D-erythrose 4-phosphate (Scheme 5.59). TA from human as well as microbial sources have been cloned.110 111 The crystal structure of the E. coliu and human112 transaldolases have been reported and its similarity to the aldolases is apparent, since it consists of an eight-stranded (o /(3)s or TIM barrel domain as is common to the aldolases. As well, the active site lysine residue that forms a Schiff base with the substrate was identified.14112 Thus, both structurally and mechanistically it is related to the type I class of aldolases. 

Suau T, Alvaro G, Benaiges MD et al. (2006) Influence of secondary reactions on the synthetic efficiency of DHAP-aldolases. Biotechnol Bioeng 93 48-55 Takayama S, McGarvey GJ, Won CH (1997) Microbial aldolases and transketolases new biocatalytic approaches to simple and complex sugars. Ann Rev Microbiol 51 285-310 Tischer W, Ihlenfeldt HG, Barzu O et al. (2001) Enzymatic synthesis of deoxyribonucleosides from deoxyribose 1-phosphate and nucleobase. Int. Patent WO014566. 

Figure 5. The biocatalytic pathway (boxed arrows) created for microbial conversion of D-glucose into cis, cw-muconate from the perspective of the biochemical pathways from which the enzymes were recruited. Conversion of D-glucose into DHS requires transketolase (tkt) from the pentose phosphate pathway and DAHP synthase (aroF, aroG, aroH)y DHQ synthase aroB and DHQ dehydratase aroD) from the common pathway of aromatic amino acid biosynthesis. Conversion of DHS into catechol requires DHS dehydratase (aroZ, enzyme A) from hydroaromatic catabolism, protocatechuate decarboxylase aroY, enzyme B), and catechol 1,2-dioxygenase (caM, enzyme C) from the benzoate branch of the p-ketoadipate pathway. (Adapted and reproduced with permission from ref. 21.)...

Regents i. Aminotransferase ii, MeCHO, transketolase iii, microbial isomerase iv, transketolase... 

The intracellular C5 carbon sugar pools oiBacillus strains comprising transke-tolase knockout mutations, which are auxotroph for aromatic amino acids, can rise to concentrations by far exceeding the physiological requirements of the bacteria. After dephosphorylation, excess ribose is excreted into the fermentation broth. Highly efficient microbial processes based on Bacillus transketolase knockout mutants were used in the past to obtain D-ribose for chemical riboflavin production at industrial level. For a review on Bacillus ribose production strains, see [311]. 

S. Takayama, G.. Mcgarvey, C.-H. Wong, Microbial aldolases and transketolases new biocata-lytic approaches to simple and complex sugars, Atmu. Rev. Microbiol. 51 (1997) 285-310. 

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