1.11.2.2	hanging drop vapor diffusion method, native MPO is crystallized with 16% (w/v) polyethylene glycol (PEG) 8000, 50 mM ammonium sulfate, 50 mM sodium acetate, 2 mM calcium acetate, and 50 mM sodium thiocyanate at 22°C and pH 5.5 for 24 h	
1.11.2.2	hanging drop vapor diffusion method, using 100 mM HEPES (pH 7.5), 150 mM NaCl, 20-25% (w/v) PEG3350	
1.11.2.2	hanging drop vapor diffusion method, using 50 mM sodium acetate (pH 5.5), 50 mM ammonium sulfate, 2 mM calcium chloride, and 22-25% (w/v) PEG 8k, at 18°C