Crystallization and preliminary X-ray analysis of porcine ribonuclease inhibitor, a protein with leucine-rich repeats.

Ribonuclease inhibitor was purified from pig liver and crystallized at 21 degrees C from solutions containing dithiothreitol as an additive and ammonium sulfate, lithium sulfate or combinations of both as precipitants. Crystals have the symmetry of the tetragonal space group I4 with a = 134.9 A and c = 83.6 A, and diffract to better than 3 A resolution. Self rotation functions and packing density of the crystals are consistent with two molecules in the asymmetric unit.