Occlusion of Ca2+ in soluble monomeric sarcoplasmic reticulum Ca2+-ATPase

Sarcoplasmic reticulum Ca2+-ATPase solubilized in monomeric form by nonionic detergent was reacted with CrATP in the presence of 45Ca2+. A Ca2+-occluded complex formed, which was stable during high performance liquid chromatography in the presence of excess non-radioactive Ca2+. The elution position corresponded to monomeric Ca2+-ATPase. It is concluded that a single Ca2+-ATPase polypeptide chain provides the full structural basis for Ca2+ occlusion.