holoenzyme (E:S or E:P) with either bound substrates (TS ES ) or product (TS EP ) or in the apoenzyme with an empty active site (apo). The electronic energies were corrected with thermal energy calculated for models with protium-only substituted Gly (re-/si-H GlyH), with either enantiomer of mono-deuterated Gly assuming transfer of either its deuterium-(re/si-D GlyH) or protium-substituent (re/si-H GlyD), and with deuterium substituting both H atoms of Gly (re/si D GlyD). For readers' convenience, the barriers associated with the respective reverse processes, i.e. transfer of H/D atoms from Gly to radical Cys are provided in the right column (R/S-H or D transfers). Note that the R-and S-enantiomers of monodeutered Gly are also represented as GlyHD and GlyDH, respectively, to aid comprehension of Fig. .