With this data analysis, our experiments led to significant observations. Interestingly, it was found that k dhβ ≈ 0.31 ± 0.03 s -1 . Moreover, the value of k dhα was essentially zero in all experiments. Thus, the direct and quantitative estimate of this feature provided by the present study confirms previous observations from dDNP experiments. Interestingly enough, the values of the enzyme kinetic rate k dhβ extracted from our experiments were actually robust and were rather insensitive to the use of prior information (see Tables 2 and SI-1), somewhat in contrast to other model parameters. Moreover, the kinetic rate values k dhα and k dhβ obtained by fitting the different realizations of the experiment agree reasonably well, as indicated in Table , which thus shows their robustness against experimental errors. Note that simultaneous fitting of the experiments lead to similar conclusions, which is illustrated in the histograms obtained from Monte Carlo simulations and depicted in Figs. SI-1 and SI-2, and in Table SI-2 in the In contrast, the analysis of k dhα was found to be essentially zero in all experiments, thereby providing direct evidence of the substrate selectivity of G6PDH towards the β anomer of G6P. Such a substrate selectivity was already pointed out in ref. . However, that study used glucose as a surrogate for G6P, and despite a ∼ 200-fold decrease of its overall activity, the enzyme was shown to have a selective action towards the glucose beta anomer. To our knowledge, the conclusion that k dhα = 0 of Salas et al. laid the basis for all subsequent models of G6P kinetic analyses, typically measured using the coupled Hexokinase-G6PDH enzymes and using glucose as a primary substrate (see for instance refs. ). Here, in contrast, our experiments provide a direct estimate of k dhα ≈ 0, to within experimental accuracy, and therefore fully justify the well accepted assumption of complete selectivity of G6PDH towards the β anomer of G6P.