3.6.1.67 apoenzyme and enzyme bound to Co2+ and Ni2+, sitting drop vapor diffusion method, using 35% (w/v) PEG 8000, 0.05 M ammonium sulfate in 50 mM Tris pH 7.5, 1 mM EDTA pH 7.4 758154 3.6.1.67 crystal structure resolved to 1.8 A resolution 728808 3.6.1.67 the structure of the enzyme is determined by X-ray diffraction, 1.8 A resolution. The best crystals grow by microseeding in sitting-drop experiments with a 1 ml reservoir solution of 1.3–1.5 M ammonium sulfate, 1% propanol, 3–5 mM DTT, 4 mM sodium diphosphate, 100 mM Na HEPES (pH 6.8). Crystals belong to monoclinic space group C2 with cell dimensions a = 124.1 A, b = 43.2 A, c = 108.0 A, and b = 115.0° 728808