The calculations for the E:P complex indicate differences of only 4 kJ/mol or less from the respective energy barriers of the E:S complex (Tab. 2, S6). Therefore, the pattern of favorable and unfavorable H or D transfer reactions is identical to that of the E:S complex with only minor differences in the ratios of the respective rates. In particular, the difference of the energy barriers for the transfer of D from Cys-SD to GlyH . between the pathways via the reand si-face is 26.4 kJ/mol which translates to a 34,200 faster rate of the former process and a very high enantioselectivity (Table ). As in the case of the E:S complex, the kinetic analysis reveals that the exchange of protium to deuterium in the glycyl radical via S-Gly829 (k S H/D) is almost 11,500 times higher (1.6 s -1 ) than via R-Gly829 (k R H/D = 1.4*10 -4 s -1 ), while in the backward exchange of deuterium to protium, the process via R-GlyHD is preferred (k R D/H = 0.26 s -1 ) compared to that via S-GlyDH (k S D/H = 5.7*10 -6 s -1 ). Similarly, as in the case of the E:S complex, the estimated rate of enzyme deuteration in D2O turns out to be 6.2 times higher than for backward protonation of the deuterated enzyme in H2O.