Abstract
Assay method for transketolase in the extract of rat liver and Escherichia coli was investigated by using the Racker's method. Pentose phosphate isomerase prepared from backer's yeast extract contained a small amount of transketolase after acetone and ammonium sulfate fractionations. However, the contaminating triose phosphate in the "isomerase product", i.e., the substrate for transketolase, obtained enzymatically from ribose-5-phosphate was reduced to the minimum by a short-time incubation(5-10 min) of the isomerase reaction. By using this substrate and a crystalline mixture of α-glycero-phosphate dehydrogenase and triose phosphate isomerase, the transketolase activities in the samples could be estimated with the change in the absorbance at 340 mμ due to NADH oxidation. The addition of Mg^<2+> and TDP to the reaction mixture was essential for E. coli extract to exhibit the full activity, while it was not necessary for rat liver extract.
