Figure shows a general view of the RutA-FMN-O2-uracil model system. Models of the reactants are presented in right side of Fig. . Fig. reproduces the features in the crystal structure PDB ID 6TEG. According to the reported results, the oxygen molecule stands closely to the N5 atom of flavin, the distance between N5 and the nearest oxygen atom is 2.09 Å. The authors of Ref. advocate the reaction mechanism of uracil oxygenation by RutA via formation of a temporary adduct with the O(oxygen)-N5(flavin) chemical bond. Correspondingly, a short distance of 2.09 Å in the reactants resolved in the crystal structure benefits this hypothesis. However, comparison of Fig. and Fig. shows a strong discrepancy between computational (3.71 ± 0.51 Å) and crystallography (2.09 Å) data for the distance between the oxygen molecule and the N5 atom of flavin. We comment that the reported value 2.09 Å for the crystallography structure PDB ID 6TEG seems to be too short for the hydrogen bond, if N5 is protonated in the reduced from of FMN, and too long for a covalent bond if one assumes a covalent binding of oxygen to the deprotonated nitrogen in FMN. We remind that location of a small molecule O2 in protein cavities is a difficult experimental task; therefore, the results of computational approaches should be taken seriously.