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. 2006 Dec 1;103(50):18917–18922. doi: 10.1073/pnas.0603650103

Fig. 3.

Fig. 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) SN2 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.