RESUMO
The stereochemistry of the transcarboxylase-catalyzed carboxylation of 3-fluoropyruvate has been studied by using fluorine NMR of unpurified reaction mixtures. When the product 3-fluorooxaloacetate was trapped by using malate dehydrogenase, only the 2R,3R diastereomer of 3-fluoromalate was formed. The fluoromethyl group of fluoropyruvate does not take up deuterium label from the solvent during the reaction. These results confirm and extend those obtained previously by Walsh and co-workers [Goldstein, J. A., Cheung, Y. F., Marletta, M. A., & Walsh, C. (1978) Biochemistry 17, 5567-5575] showing that transcarboxylase is specific for one of the two prochiral hydrogens in fluoropyruvate. Transcarboxylase, coupled to malate dehydrogenase, has been used to analyze samples of chiral fluoropyruvate obtained by dephosphorylation of (Z)-fluorophosphoenolpyruvate in D2O in the presence of either pyruvate kinase or enzyme I from the Escherichia coli sugar transport systems. Analysis of the fluoromalate produced showed that fluoroenolpyruvate is deuterated from opposite faces by these two enzymes: enzyme I protonates (deuterates) fluoroenolpyruvate exclusively from the 2-re face and pyruvate kinase does so mainly from the 2-si face. Fluoropyruvate is carboxylated by transcarboxylase with absolute retention of configuration.