Crystallization of an enzyme‐inhibitor complex: Proteinase K with its protein inhibitor, PK13

Crystals of a complex of proteinase K (molecular mass, 28,790 Da) with its naturally occurring protein inhibitor PK13 (19,641 Da), have been prepared by a microdialysis technique and modified by hanging drop vapor diffusion against 25% ammonium sulfate in 50 mM Tris‐HCl, pH 7.8. The crystals are long prisms with diamond‐shaped cross sections of 0.2 × 0.4 × 1.5 mm 3 and they diffract X‐rays to a resolution of 2.5 Å. They belong to the orthorhombic space group P 2 1 2 1 2 1 with cell dimensions a = 64.1 Å, b = 66.8 Å, and c = 133.8 Å. Assuming one whole complex in the asymmetric unit, one obtains V M = 2.95 Å 3 /Da and the solvent content, V solv = 58.3%. © 1994 Wiley‐Liss, Inc.