Production of Glycolate by Oxidation of the 1,2‐Dihydroxyethyl‐thiamin‐diphosphate Intermediate of Transketolase with Hexacyanoferrate(III) or H2O2

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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).

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