Deuteration of certain positions influences the heights of the energetic barriers of the respective transition states of H/D exchange pathways through primary and secondary kinetic isotope effects (KIE). Therefore, we analyzed all possible scenarios separately, i.e. when the H of the Gly829 radical is exchanged to D, when the D is exchanged back to H, and when Gly829 stays either fully protonated or deuterated, all in both possible geometries via either the re or the si face of the radical Gly (Table , Table , S8). Moreover, we did these calculations with three different forms of BSS: the enzyme in complex with the substrates (E:S), with the products (E:P), or as an apoenzyme with an empty active site cavity (apo).