Stereochemical investigation of the phosphoketolase reaction. The formation of chiral [2H1,3H]acetyl phosphate.

1. D-(1R)-(1-2H1)[1-3H]Fructose 6-phosphate was prepared by the action of glucosephosphate isomerase on D-(1-2H)glucose 6-phosphate in tritiated water. Using the same enzyme but interchanging the labelling pattern of the substrate D-(1S)-(1-2H)[1-3H]fructose 6-phosphate was also obtained. 2. The doubly labelled samples of D-fructose 6-phosphate were converted into chiral acetylphosphate on phosphoketolase from Bifidium globosum (ATCC 25864), and these were reacted in situ with phosphotransacetylase and malate synthase in the presence of coenzyme A and glyoxylate. 3. The steric distribution of the tritium in the samples of malate, as shown by the action of fumarase, revealed that D-(1R)- and D-(1S)-(1-2H1)[1-3H]fructose 6-phosphate was converted into (R)- and (S)-(2H1)[3H]acetyl-phosphate, respectively. 4. The results are discussed in terms of the mechanism of action of phosphoketolase.