Enzymatic syntheses of ketoses: study and modification of the substrate specificity of the transketolase from Saccharomyces cerevisiae

Transketolase (TK) is a useful catalyst for ketose syntheses. The first part of this paper reports a convenient and easy method to synthesise 4-deoxy--fructose-6-phosphate, potential inhibitor of sugar metabolism. TK used in synthetic purposes is the enzyme from Saccharomyces cerevisae, which is commercially available, or the enzyme from spinach leaves which we obtained as a crude extract. But these sources are expensive or give small quantities of the enzyme. In order to obtain larger amounts of enzyme, we use TK overexpressed in S. cerevisiae. The three-dimensional structure being known, the study and modification of the substrate specificity of this enzyme can be investigated by site-directed mutagenesis. In the second part of this paper, our study shows that Asp 477 is involved in determining the stereospecificity towards C2 hydroxyl group of the acceptor substrate.