Fig. 8.

Proposed NocTE catalytic mechanism. a The proposed sequence of transthiolation, epimerization, and hydrolysis steps catalyzed by NocTE is depicted. The residues that comprise the binding pockets for the L-Hpg and D-Hpg are indicated with the dashed and solid curves, respectively. The movement of the His1808 side chain that accompanies epimerization is also represented. b Illustration of attack and aging of the FP probe. The boxed structure is observed in the crystal and represents the species directly above it in (a), highlighting how the phosphonate oxygens mimic the oxyanion hole and the attacking water molecule in the hydrolysis step