A Bowman–Birk type trypsin inhibitor I‐2,Mr= 14 000, 123 amino‐acid residues, isolated from wheat germ, and its complex with trypsin have been crystallized. For I‐2 two morphologically different crystal forms were obtained. Crystal form 1 is tetragonal,P4122 orP4322, witha= 55.45 (2),c= 129.1 (2) Å andV= 3.97 (2) × 105 Å3. The crystals diffract X‐rays very anisotropically, to less than 6 Å resolution normal to thec* direction, but up to 3 Å resolution in the other directions. Crystal form 2 is monoclinic, space groupC2. The cell parameters show significant variation even for crystals in the same batch. The median parameters are:a= 83.9,b= 41.5,c= 45.7 Å, β = 95.9° andV= 1.58 × 105 Å3. The diffraction pattern is isotropic and reflections up to 2.2 Å resolution were observed. The crystals of the complex between bovine trypsin and I‐2 (2:1) belong to the orthorhombic space groupP212121witha= 73.49 (2),b= 120.56 (3),c= 70.04 (2) Å andV= 6.206 (5) × 105 Å3. The crystals diffract up to 2.3 Å resoluti
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