title: Production of glycolate by oxidation of the 1,2-dihydroxyethyl-thamin-diphosphate intermediate of transketolase with hexacyanoferrate(III) or H2O2.
abstract: In the presence of hexacyanoferrate(III), or other suitable oxidants, transketolase catalyzes the oxidative cleavage of its donor substrates xylulose 5-phosphate or fructose 6-phosphate into glycolate and glyceraldehyde 3-phosphate or erythrose 4-phosphate, respectively. Two moles of hexacyanoferrate(III) are reduced per mole of oxidatively cleaved donor substrate. In analogy to the oxidative trapping of carbanion intermediates of other enzymes [Healy, M. J. & Christen, P. (1973) Biochemistry, 12, 35-41], the kinetic features of the reaction indicate that the 1,2-dihydroxyethylthiamin diphosphate intermediate is the oxidation-susceptible species. The molecular activity for the oxidative cleavage of fructose 6-phosphate at a hexacyanoferrate(III) concentration of 0.5 mM is 0.2% of that for the normal transfer reaction with erythrose 4-phosphate as acceptor substrate. Glycolate is also produced with H2O2 as oxidant; however, the reaction is at least two orders of magnitude slower than with hexacyanoferrate(III).
mesh_terms: D005292:Ferricyanides; D006016:Glycolates; D006861:Hydrogen Peroxide; D007700:Kinetics; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013835:Thiamine Pyrophosphate / Q000031:analogs & derivatives*; D014174:Transketolase / Q000378:metabolism*
chemical_list: D005292:Ferricyanides; D006016:Glycolates; C007931:hexacyanoferrate III; D006861:Hydrogen Peroxide; D014174:Transketolase; D013835:Thiamine Pyrophosphate