Figure 3
(a) 144 crystallization experiments were set up using a mother liquor containing 10 mg ml−1 hen egg-white lysozyme in 20 mM sodium acetate pH 4.6, 1 M NaCl, in volumes of 1, 2, 4, 8, 16, 32, 64, 128 and 256 nl (all in 16-fold). In the smaller volumes (1–8 nl) needle-shaped crystals predominated (see also Fig. 2), whereas in the larger volumes bulky tetragonal crystals appeared. The graph shows the average number of tetragonal crystals per droplet that appeared after 24 h as a function of the volume of the droplet. The straight line is a linear fit: (number of crystals) = 0.5 + 0.011 nl−1 × (volume of droplet), with a correlation coefficient of 0.95. (b) In the experiment described in (a), needle-shaped crystals appeared predominantly in the smaller volumes. The frequency with which these crystals appeared within 24 h is plotted as a function of the surface-to-volume ratio of the droplets, assuming a spherical shape. Note that in the larger surface-to-volume ratios (corresponding to the 1, 2 and 4 nl droplets) we still always found crystals, but these were mostly of the `sea-urchin' type. |