Stereochemistry of the re-citrate-synthase reaction.

1 R-Acetate and S-acetate, as the coenzyme-A esters, were converted into citrates on recitrate synthase. 2 The citrate were assayed for chirality at the 2-position (a) by incubation with aconitate hydratase (aconitase) and (b) by cleavage to malate by citrate lyase combined with malate dehydrogenase, followed by incubation of the isolated malate with fumarate hydratase (fumarase). 3 In each case, the citrate (or malate) derived from R-acetate retained most of its tritium, and the citrate (or malate) derived from S-acetate lost most of its tritium, on incubation with the hydratase. 4 It was concluded that if a normal intramolecular deuterium-isotope effect is operative, the condensation of oxaloacetate with acetyl-coenzyme A on re-citrate synthase proceeds with inversion of configuration at the methyl group.