X-ray diffraction studies of troponin-C crystals from rabbit and chicken skeletal muscles

Crystals of troponin-C from rabbit and chicken muscles have been obtained using the vapor diffusion method. Crystals of rabbit troponin-C are tetragonal with a unit cell of a = b = 89.4 A, c = 79.9 A, space group P42, and 4 molecules/asymmetric unit. Diffraction from these crystals is limited to 7A and the crystals are unstable under x-ray irradiation, making them unsuitable for a high resolution structural determination. Crystals of chicken troponin-C are trigonal with a unit cell of a = b = 66.7 A, c = 60.8 A. The space group is P3121 or P3221 and there is only 1 molecule/asymmetric unit. These crystals diffract to at least 2.2 A, are very stable under x-ray irradiation, and are suitable for high resolution study.