2.1.1.300 purified recombinant native and selenomethionine-substituted wild-type and mutant H206A enzymes in complex with S-adenosyl-L-methionine, of wild-type apoenzyme, and of wild-type enzyme in complex with S-adenosyl-L-homocysteine (SAH) or with SAH and tetrahydropapaverine, hanging drop vapour diffusion method, mixing of 0.0015 ml of protein solution with 0.0015 ml of reservoir solution containing 340 g/l pentaerythritol ethoxylate (15:4 EO/OH), 50 mM bis-Tris-HCl, pH 6.0, 70 mM ammonium sulfate, and 160 g/l glycerol, and equilibration against 0.45 ml of reservoir solution at 22°C, 1-3 weeks, for the complex crystals, the enzyme is incubated with the ligands (0.75 mM THP oand/or 1 mM SAM/SAH) before crystallization, method optimization, X-ray diffraction structure determination and analysis at 1.6-2.3 A resolution 757162 2.1.1.300 sitting-drop vapour-diffusion method, hanging-drop vapour-diffusion method at 16°C, crystallized in space group P2(1). The structure is solved at 2.0 A resolution using a xenon derivative and the single isomorphous replacement with anomalous scattering method 723837