   2.1.1.245 | a [methyl-Co(III) corrinoid Fe-S protein] + tetrahydrosarcinapterin = a [Co(I) corrinoid Fe-S protein] + 5-methyltetrahydrosarcinapterin |
random Bi-Bi mechanism of transfer of the methyl group from (6S)-methyltetrahydrofolate to the corrinoid/iron-sulfur protein: CH3-H4folate binds to MeTr in the unprotonated form and then undergoes rapid protonation. This protonation enhances the electrophilicity of the methyl group, in agreement with a 10fold increase in the pKa at N5 of CH3-H4folate. Next, the Co(I)-CFeSP attacks the methyl group in a rate-limiting SN2 reaction to form methylcob(III)amide. Finally, the products randomly dissociate. A pH-dependent conformational change is required for methyl transfer in the forward and reverse directions, a rate-limiting ionization of MeTr, not of CH3-H4folate, is responsible for the pH dependence of the methyl transfer reaction |
717236 |
