| Type: | Binding_site | Name: | Transketolase binding site |
| Description: | Transketolase (TK) catalyzes the reversible transfer of a two-carbon ketol unit from xylulose 5-phosphate to an aldose receptor, such asribose 5-phosphate, to form sedoheptulose 7-phosphate and glyceraldehyde 3- phosphate. This enzyme, together with transaldolase, provides a link betweenthe glycolytic and pentose-phosphate pathways. TK requires thiamine pyrophosphate as a cofactor. In most sources where TK hasbeen purified, it is a homodimer of approximately 70 Kd subunits. TK sequences from a variety of eukaryotic and prokaryotic sources [, ] show that theenzyme has been evolutionarily conserved. In the peroxisomes of methylotrophic yeast Pichia angusta(Yeast) (Hansenula polymorpha), there is a highly related enzyme, dihydroxy-acetone synthase (DHAS) (also known as formaldehyde transketolase), which exhibits a very unusualspecificity by including formaldehyde amongst its substrates.1-deoxyxylulose-5-phosphate synthase (DXP synthase) [] is an enzyme so farfound in bacteria (gene dxs) and plants (gene CLA1) which catalyzes the thiamine pyrophosphoate-dependent acyloin condensation reaction between carbonatoms 2 and 3 of pyruvate and glyceraldehyde 3-phosphate to yield 1-deoxy-D- xylulose-5-phosphate (dxp), a precursor in the biosynthetic pathway toisoprenoids, thiamine (vitamin B1), and pyridoxol (vitamin B6). DXP synthase is evolutionary related to TK. The N-terminal section, contains a histidine residue which appears to function in proton transfer during catalysis []. In the centralsection there are conserved acidic residues that are part of the active cleft and may participate in substrate-binding [].This family includes transketolase enzymes and also partially matches to 2-oxoisovalerate dehydrogenase beta subunit . Both these enzymes utilise thiamine pyrophosphate as a cofactor, suggestingthere may be common aspects in their mechanism of catalysis.This entry is located in the central section and contains conserved acidic residues that are part of the active cleft and may participate in substrate-binding []. | Short Name: | Transketolase_BS |
