Investigation of the second question requires an analysis of the kinetic equations for the Ping- Although our analysis is approximate, it demonstrates that it is possible to observe KIE in the steady-state experiment, even when the process related to OHR is a hundred times slower than the RHR. Based on our preliminary pre-steady-state kinetics, we expect that at an optimal pH of 6.5 OHR should be at least 10 times slower than RHR, which would explain the experimental KIE in the range of 1.05-1.33. We have seen a similar masking effect in our recent study of KstD1, but kOHR and kRHR were estimated as of the same magnitude . As a result, we observed higher values of the steady-state KIE for KstD1 (1.28 for 17-MT and 1.5 for DHT) than for AcmB (1.06-1.17 for 17-MT and 1.05-1.33 for DHT).