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Figure 9.
Figure 9. The reaction mechanism of the interconversion of
(2S)-methylacyl-CoA to (2R)-methylacyl-CoA by MCR, as suggested
from the crystal structure and kinetic data. In this enzymatic
conversion, His126 acts as a general base (abstracting a proton
from the α-carbon atom of the (S)-compound) and Asp156 acts
as a general acid (donating a proton to the α-carbon atom of
the (S)-compound). Dotted lines highlight important stabilizing
interactions. The oxyanion of the reaction intermediate is
stabilized by hydrogen bonding interactions with the main-chain
NH group of Asp127, as well as with the protonated side-chains
of His126 and Asp156.
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