Yeast transketolase, in addition to catalyzing the transferase reaction through utilization of two substrates-the donor substrate (ketose) and the acceptor substrate (aldose)-is also able to catalyze a one-substrate reaction with only aldose (glycolaldehyde) as substrate. The interaction of glycolaldehyde with holotransketolase results in formation of the transketolase reaction intermediate, dihydroxyethyl-thiamin diphosphate. Then the glycolaldehyde residue is transferred from dihydroxyethyl-thiamin diphosphate to free glycolaldehyde. As a result, the one-substrate transketolase reaction product, erythrulose, is formed. The specific activity of transketolase was found to be 0.23 U/mg and the apparent K-m for glycolaldehyde was estimated as 140 mM. (C) 2003 Published by Elsevier Inc.