where r a , r b are the relaxation rates of the α and β 13 C anomer polarizations; k α , k β are the anomer exchange rates; k dhα and k dhβ are the enzyme reaction rates for both G6P anomers, and r l is an empirical "leakage" rate that takes into account the C carbonyl relaxation rate of the δ-PGL as well as the isomerisation with γ-PGL and their degradation into 6-phosphogluconic acid (6PGA). 9;15 With the aim of retrieving quantitative kinetic parameters from dDNP experiments, it is important to assess the robustness of the experimental setup, which implies that repeated experiments are equally well fitted with the same sets of parameters. Therefore, and in order to test the robustness of the experimental protocol, the experiment was performed in triplicate. Prior to the analysis of chemically relevant parameters, the relevant quantities that allow one to address this question are the eigenmodes and eigenvectors of the differential system of Eqs.1, which were therefore analyzed to compare the kinetic information embodied in the different experiments. Since the decay rate r l is an obvious root of the characteristic equation: