3-dimensional (type I) microcrystals of detergent-solubilized (Na+, K+)-ATPase enzyme from pig kidney

3-dimensional crystalline arrays (Type I) of the ion transporting (Na+, K+)-ATPase enzyme from pig kidney develop in detergent-solubilized crude membrane-fragments or purified (Na+, K+)-ATPase preparations upon exposure to 0.1 M KCl and 0.1 M NaCl at pH 7.4 for several days at 2 degrees C in a crystallization medium that preserves the ATPase activity. Crystallization was obtained with non-ionic detergents; C12E8, C12E9, C12E10, and BRIJ 36 at a detergent: protein.ratio ranging from 1.8:1 to 4.4:1 in purified (Na+, K+)-ATPase preparations. High concentration of glycerol (40% v/v), Mg2+ ions and low temperature proved to be essential for crystallization and for protection of ATPase activity. Cross-linking of (Na+, K+)-ATPase crystals with glutaraldehyde protects the crystalline structure under conditions which otherwise disrupt the preformed crystals. The new crystals show close resemblance to the 3-dimensional crystals of the Ca(2+)-ATPase featuring the same structure of stacked lamellae. High-resolution electron microscopy of frozen-hydrated (Na+, K+)-ATPase samples is in progress to give unit cell dimensions and molecular packing of the new crystals.