Crystallizations and preliminary X-ray studies of calotropins DI and DII

Abstract

Crystals of calotropin DI ( M r 23,400), have been prepared by microdialysis against 5% (w/v) polyethylene glycol 20,000 in water, pH 7.0. They have orthorhombic space group P2 12 12 1 with cell parameters a = 57.5 A ̊ , b = 86.2 A ̊ , c = 40.3 A ̊ . Crystals of calotropin DII ( M r 24,000), prepared by the same technique against 5% (w/v) polyethylene glycol 20,000 in phosphate buffer of low ionic strength, pH 7.0, display monoclinic space group C2 with cell parameters a = 135.8 A ̊ , b = 32.0 A ̊ , c = 47.7 A ̊ , β = 103.80 ° . In both cases, there is only one molecule in the asymmetric unit.