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Equilibrium Isotope Effects on the Crotonase Reaction

Kołodziejska-Huben M., Anderson V. E., Paneth P.

Polish Journal of Chemistry

2002

Vol. 76 / nr 10

1467-1480

Equilibrium isotope effects on the enoyl-CoA hydratase (crotonase, ECH) - catalyzed reaction were modeled by a mixed QM/MM method. The classical region (27 aminoacids essential for the catalysis) was treated at the MM level using universal force field UFF. The quantum atoms of 4-(N,N-dimethylamino)cinnamoyl-CoA (DAC-CoA), one water molecule, and two glutamate residues (Glu164 and Glu144) in the active site were treated at the PM3 level.

DFT/PM3 study of the enoyl-CoA hydratase catalyzed reaction

Pawlak J., Bahnson B., Anderson V.

Nukleonika

2002

Vol. 47,suppl.1

33-36

The enoyl-CoA hydratase catalyzed hydration of alfa,beta-unsaturated thiolesters has been modeled by using the crystal structure of 4-(N,N-dimethylamino)cinnamoyl-CoA bound at the active site. The quantum chemical calculation used the ONIOM mixed level procedure to permit the substrate thiolester and water molecule to be modeled using B3LYP/6-31G(d) level of theory and the active site residues modeled at a semiempirical level using the PM3 Hamiltonian. The results permitted the identification of a stable thiolester enolate intermediate, supporting a stepwise reaction mechanism. The calculation also suggests that the same proton removed from the nucleophilic water molecule is transferred to C alfa in the subsequent protonation of the enolate intermediate. This observation reconciles the stepwise mechanism with the previously reported double isotope effect study [3].