(-)-secoisolariciresinol + 2 NAD+ |
nicotinamide and the substrate are in the proper orientation for the well established B-face-specific hydride transfer to C-4 from the corresponding substrate reaction center, crystallization data. The Lys171 residue lowers the pKa of the phenolic hydroxyl group of the Tyr167 in the catalytic triad together with the positively charged NAD+. The Ser153 residue then shares its proton with the phenolic anionic group of Tyr167, and in this way, the latter can serve as a general base in substrate deprotonation during catalysis. Concomitant deprotonation of the (-)-secoisolariciresinol is then presumed to occur via the phenolic anion of Tyr167 with hydride transfer to NAD+, followed by nucleophilic attack to form the (-)-lactol intermediate from (-)-secoisolariciresinol. Subsequent dehydrogenation of the (-)-lactol can then occur by the same process involving Tyr167 as before and a newly bound NAD+ molecule to afford the dibenzyl furanone, (-)-matairesinol |
Podophyllum peltatum |
(-)-matairesinol + 2 NADH + 2 H+ |
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