A preliminary crystallographic investigation of rabbit muscle creatine kinase

Abstract

Three crystal forms of rabbit muscle creatine kinase have been grown, one of which seems suited to a high resolution X-ray diffraction study. The first form is of monoclinic space group P2 1 with a = 54 A ̊ , b = 114 A ̊ , c = 145 A ̊ , β = 91 ° and has as the asymmetric unit two molecules of total molecular weight 160, 000. The second form, grown in the presence of mercurials, is of space group A2 with a = 52 A ̊ , b = 165 A ̊ , c = 237 A ̊ , β = 91 ° and also has two molecules in the asymmetric unit. The third crystal form, grown in the presence of a high concentration of cysteine, is of apparent space group P2 12 12 1, but evidence indicates that the true space group may be P2 122 1. The dimensions of the orthorhombic unit cell are a = 47 A ̊ , b = 86 A ̊ , c = 125 A ̊ , and the asymmetric unit contains a single protein subunit. Assuming the latter space group, then the creatine kinase molecule possesses a twofold axis relating two identical subunits.