Cryoprotective efficacy of methylamine osmolytes as post-growth treatments. Shown are diffraction images of cryocooled tetragonal thermolysin after 30–60 s soaks as described in §2. (a) Cryosolution composed of 1 M TMAO, 1 M NaCl and 0.1 M MES (see §2). Powder rings for ice Ic are visible and the protein diffraction limit is 3.3 Å. (b) Cryosolution using 3 M TMAO. The diffraction limit is now approximately 2.1 Å. (c) Cryosolution using 4 M sarcosine, giving a diffraction limit of ∼2.1 Å (1 M sarcosine yielded ∼3.5 Å diffraction). (d) Cryosolution using 3 M betaine, giving a diffraction limit of ∼2.4 Å (1 M betaine yielded ∼3.6 Å diffraction).