Schenk, Gerhard and Duggleby, Ronald
Properties and functions of the thiamin diphosphate
dependent enzyme transketolase.
The International Journal of Biochemistry & Cell Biology, 30.
This review highlights recent research on the properties and functions of the enzyme transketolase, which requires
thiamin diphosphate and a divalent metal ion for its activity. The transketolase-catalysed reaction is part of the
pentose phosphate pathway, where transketolase appears to control the non-oxidative branch of this pathway,
although the overall ¯ux of labelled substrates remains controversial. Yeast transketolase is one of several thiamin
diphosphate dependent enzymes whose three-dimensional structures have been determined. Together with
mutational analysis these structural data have led to detailed understanding of thiamin diphosphate catalysed
reactions. In the homodimer transketolase the two catalytic sites, where dihydroxyethyl groups are transferred from
ketose donors to aldose acceptors, are formed at the interface between the two subunits, where the thiazole and
pyrimidine rings of thiamin diphosphate are bound. Transketolase is ubiquitous and more than 30 full-length
sequences are known. The encoded protein sequences contain two motifs of high homology; one common to all
thiamin diphosphate-dependent enzymes and the other a unique transketolase motif. All characterised transketolases
have similar kinetic and physical properties, but the mammalian enzymes are more selective in substrate utilisation
than the nonmammalian representatives. Since products of the transketolase-catalysed reaction serve as precursors
for a number of synthetic compounds this enzyme has been exploited for industrial applications. Putative mutant
forms of transketolase, once believed to predispose to disease, have not stood up to scrutiny. However, a
modi®cation of transketolase is a marker for Alzheimer's disease, and transketolase activity in erythrocytes is a
measure of thiamin nutrition. The cornea contains a particularly high transketolase concentration, consistent with
the proposal that pentose phosphate pathway activity has a role in the removal of light-generated radicals.
||Thiamin diphosphate; Transketolase; Pentose phosphate pathway; Kinetics; Thiamin defciency;
||Science & Engineering > Chemistry
||28 May 2012 15:04
|Journal or Publication Title:
||The International Journal of Biochemistry & Cell Biology
||Elsevier Science Ltd.
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