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Figure 3.
Proposed mechanism of methanol activation. (A) Scheme of a
unique acidic cluster that flanks the zinc and methanol-binding
site. The acidic residues (in red) might play a crucial role in
polarizing zinc(II) and methanol. The unclear peak X was
tentatively assigned as a potassium ion. Methanol is modeled
into the protein, and its distance to the corrinoid Co is
estimated based on the distance between the zinc(II) and
methanol oxygen of 2 Å. (B) S[N]2 mechanism for the
methylation of 5-hydroxybenzimidazolyl cob(I)amide with
methanol. The methanol is activated by the strong electrophile
zinc(II) and attacked by the supernucleophile cob(I)amide.
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