1.7.3.6	purified native enzyme, mixing of 0.002 ml of protein in 20 mM Tris-HCl, pH 8.1, with 0.002 ml of crystallization solution containing 0.1 M potassium nitrate, 0.1 M MES-Na buffer, pH 7.5, and 46% v/v PEG 400, X-ray diffraction structure determination and analysis at 2.1 A resolution, modelling