Crystals of recombinant wild-type antichymotrypsin have been prepared by the method of vapor diffusion with polyethylene glycol 4000 as a precipitant at pH 5.7. Two crystal forms are observed. One form belongs to tetragonal space group P43212 (or P41212) and has unit cell dimensions a = b = 126 A , c = 243 A , with two molecules in the asymmetric unit. The other crystal form belongs to orthorhombic space group P212121 and has unit cell parameters of a = 73 A , b = 78 A and c = 80 A , with one molecule in the asymmetric unit. Diffraction intensity measurements have been made on the tetragonal crystal form to a limiting resolution of 4.1 A, and reflections have been observed on X-ray still photographs to a limiting resolution of 2.5 A for the orthorhombic form. An activity assay of redissolved tetragonal form crystals indicates that the uncleaved, functional serpin has been crystallized.
