Evidence for an intramolecular, stepwise reaction pathway for PEP phosphomutase catalyzed phosphorus-carbon bond formation
摘要:
The Tetrahymena pyriformis enzyme, phosphoenolpyruvate phosphomutase, catalyzes the rearrangement of phosphoenolpyruvate to the P-C bond containing metabolite, phosphonopyruvate. To distinguish between an intra- and intermolecular reaction pathway for this process an equimolar mixture of [P-O-18,C(2)-O-18]thiophosphonopyruvate and (all O-16) thiophosphonopyruvate was reacted with the phosphomutase, and the resulting products were analyzed by P-31 NMR. The absence of the cross-over product [C(2)-O-18]thiophosphonoenolpyruvate in the product mixture was interpreted as evidence for an intramolecular reaction pathway. To distinguish between a concerted and stepwise intramolecular reaction pathway the pure enantiomers of the chiral substrate [O-18]thiophosphonopyruvate were prepared and the stereochemical course of their conversion to chiral [O-18]thiophosphoenolpyruvate was determined. The assignments of the phosphorus configurations in the [O-18]thiophosphonopyruvate enantiomers reported earlier (McQueney, M. S.; Lee, S.-l.; Bowman, E.; Mariano, P. S.; Dunaway-Mariano, D. J. Am. Chem. Soc. 1989, 111, 6885-6887) were revised according to the finding that introduction of the O-18 label into the thiophosphonopyruvate precursor occurs with retention rather than with (the previously assumed) inversion of configuration. On the basis the observed conversion of (S(p))-[O-18]thiophosphonopyruvate to (S(p))-[O-18]thiophosphoenolpyruvate and (R(p))-[O-18]thiophosphonopyruvate to (Rp)-[O-18]thiophosphoenolpyruvate, it was concluded that the PEP phosphomutase reaction proceeds with retention of the phosphorus configuration and therefore by a stepwise mechanism. Lastly, the similar reactivity of the oxo- and thio-substituted phosphonopyruvate substrates (i.e., nearly equal V(max)) was interpreted to suggest that nucleophilic addition to the phosphorus atom is not rate limiting among the reaction steps.
Evidence for an intramolecular, stepwise reaction pathway for PEP phosphomutase catalyzed phosphorus-carbon bond formation
摘要:
The Tetrahymena pyriformis enzyme, phosphoenolpyruvate phosphomutase, catalyzes the rearrangement of phosphoenolpyruvate to the P-C bond containing metabolite, phosphonopyruvate. To distinguish between an intra- and intermolecular reaction pathway for this process an equimolar mixture of [P-O-18,C(2)-O-18]thiophosphonopyruvate and (all O-16) thiophosphonopyruvate was reacted with the phosphomutase, and the resulting products were analyzed by P-31 NMR. The absence of the cross-over product [C(2)-O-18]thiophosphonoenolpyruvate in the product mixture was interpreted as evidence for an intramolecular reaction pathway. To distinguish between a concerted and stepwise intramolecular reaction pathway the pure enantiomers of the chiral substrate [O-18]thiophosphonopyruvate were prepared and the stereochemical course of their conversion to chiral [O-18]thiophosphoenolpyruvate was determined. The assignments of the phosphorus configurations in the [O-18]thiophosphonopyruvate enantiomers reported earlier (McQueney, M. S.; Lee, S.-l.; Bowman, E.; Mariano, P. S.; Dunaway-Mariano, D. J. Am. Chem. Soc. 1989, 111, 6885-6887) were revised according to the finding that introduction of the O-18 label into the thiophosphonopyruvate precursor occurs with retention rather than with (the previously assumed) inversion of configuration. On the basis the observed conversion of (S(p))-[O-18]thiophosphonopyruvate to (S(p))-[O-18]thiophosphoenolpyruvate and (R(p))-[O-18]thiophosphonopyruvate to (Rp)-[O-18]thiophosphoenolpyruvate, it was concluded that the PEP phosphomutase reaction proceeds with retention of the phosphorus configuration and therefore by a stepwise mechanism. Lastly, the similar reactivity of the oxo- and thio-substituted phosphonopyruvate substrates (i.e., nearly equal V(max)) was interpreted to suggest that nucleophilic addition to the phosphorus atom is not rate limiting among the reaction steps.