Evidence for an intramolecular, stepwise reaction pathway for PEP phosphomutase catalyzed phosphorus-carbon bond formation
作者:Michael S. McQueney、Sheng Lian Lee、William H. Swartz、Herman L. Ammon、Patrick S. Mariano、Debra Dunaway-Mariano
DOI:10.1021/jo00025a031
日期:1991.12
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.