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Figure 3.
Figure 3. Schematic representation of the proposed
aminomethyltransfer reaction catalyzed by T-protein. The bound
H[4]folate attacks the methylene carbon of the aminomethyl
lipoate arm attached to H-protein via the nucleophilic N10 group
putatively with concomitant proton abstraction by Asp101 and
ammonia release. The resulting covalent intermediate is attacked
by the N5 group with concomitant deprotonation of the N5 by the
sulfur group of the nascent dihydrolipoate. An alternative
possibility is that the N5 group attacks first, followed by the
attack of the N10 group.
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