Crystallization of porcine liver ribonuclease inhibitor a member of the family of proteins containing leucine-rich repeats.

Single crystals of the RNase inhibitor from porcine liver have been obtained from 30 to 34% saturated ammonium sulphate solutions at pH 6.0 to 7.2, containing 20 mM dithiothreitol, at room temperature over a period of two to three weeks. Because the inhibitor contains 30 1/2-cystinyl residues, all of which occur in the free thiol form, crystallization experiments were carried out in a desiccator under a nitrogen atmosphere. The crystals belong to the tetragonal space group I4, with cell dimensions a = b = 134.76 A and c = 83.65 A. The asymmetric part of the unit cell contains two molecules with a molecular mass of 49,093 Da, as could be shown with a self-rotation function calculated in the resolution range 10.0 to 3.2 A. The crystals diffract to at least 3.2 A resolution and are suitable for an X-ray structure determination.