Xenon sites in hen egg-white lysozyme. (a) Xe1 and Xe2 are commonly observed sites. Xe3 and Xe4 were newly found in the present study. Xe4 is found only in the crystals cooled under pressurization. The A and B sites were reported previously but not observed in our study. (b)–(e) Electron density and difference Fourier maps around the xenon sites. Green, orange and blue meshes indicate Bijvoet-difference Fourier using the diffraction data of a crystal under 2 MPa pressurization, a gas released crystal and a native crystal, respectively. Blue sticks indicate symmetry-related molecules. Brown numbers and dots indicate close contacts to the xenon atoms.