Irradiation damage of catalase crystals. The fading of the intensities of the diffraction spots (4, 30) is plotted as a function of the accumulated electron dose. This plot demonstrates that a further reduction of the specimen temperature from liquid-nitrogen to liquid-helium temperature results in an improvement of the cryo-protection factor by two or more. [Reproduced with permission from Fig. 4 of Fujiyoshi (1998), Adv. Biophys. 35, 25–80.] Vertical axis: relative intensity of diffraction spot; 1.0 on scale = 100%. Horizontal axis: total accumulated radiation dose in e Å−2; the dotted line at 0.37 is placed at 1/e, which often is used for determining the critical dose.