1.13.11.48 N-terminally His6-tagged HOD is crystallized by the hanging-drop vapour-diffusion method using sodium/potassium tartrate as a precipitant and CuCl2 as an additive. The structure is solved by the single anomalous dispersion technique using data collected to 3.5 A resolution at the Cu absorption peak wavelength. The crystals belong to the primitive tetragonal space group P43212, with unit-cell parameters a = b = 153.788, c = 120.872 A 1.13.11.48 purified recombinant wild-type and mutants C69S and C69S/H251A N-terminally His6-tagged HOD, hanging drop vapour diffusion method, 50 mg/ml protein in 20 mM Tris-HCl pH 7.5, 100 mM NaCl, 2 mM EDTA, 1 mM DTT, is mixed with 1.65 M sodium/potassium tartrate, 0.1 M HEPES, pH 7.0, and 30 mM CuCl2, method optimization, X-ray diffraction structure determination and analysis at 3.5 A resolution, single anomalous dispersion technique 1.13.11.48 random-acceleration molecular dynamics study on 3-hydroxy-2-methylquinolin-4-one 2,4-dioxygenase in complex with its natural substrate, 3-hydroxy-2-methylquinolin-4(1H)-one, in aqueous solution. Gates for expulsion of O2 from the protein, which can also be taken as gates for O2 uptake, are found throughout almost the whole external surface of the protein, alongside a variety of binding pockets for O2 . The most exploited gates and binding pockets do not correspond to the single gate and binding pocket proposed from the examination of the static model from X-ray diffraction analysis