The presence of a hydroxyl group at the C-1 atom of the transketolase substrate molecule is necessary for the enzyme to perform the transferase reaction.
Transketolase catalyzes the transfer of an aldehyde residue from keto sugars to aldo sugars. The intermediate product is dihydroxyethylthiamine pyrophosphate (DHETPP). In the absence of an acceptor substrate, the reaction is stopped at this stage and DHETPP does not undergo subsequent transformations. Pyruvate decarboxylase catalyses pyruvate decarboxylation to yield free aldehyde. The intermediate product is hydroxyethylthiamine pyrophosphate (HETPP). It differs from DHETPP only in that it has no hydroxyl at the C-2 atom of the aldehyde residue. We have shown that transketolase can bind HETPP and split the aldehyde residue from it. This fact suggests that the path of the reaction is determined by the absence (in HETPP) or presence (in DHETPP) of a hydroxyl group. In the former case the reaction will yield free aldehyde, in the latter the aldehyde residue will be transferred onto an acceptor substrate.
D001051:Apoenzymes / Q000378:metabolism; D002942:Circular Dichroism; D006900:Hydroxylation; D007700:Kinetics; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013379:Substrate Specificity; D013835:Thiamine Pyrophosphate / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D014174:Transketolase / Q000737:chemistry / Q000378:metabolism*
D001051:Apoenzymes; C093420:dihydroxyethylthiamine pyrophosphate; C047467:2-(1-hydroxyethyl)thiamine pyrophosphate; D014174:Transketolase; D013835:Thiamine Pyrophosphate