The 11 angstrom resolution projection map of Na+/K+-ATPase calculated by application of single particle analysis to two-dimensional crystal images

Two-dimensional (2D) crystals of Na+/K+-ATPase were vitrified and observed with an electron cryo-microscope that allowed specimen observation at liqui d helium temperature. Images showing 19 Angstrom spots on the optical diffr action patterns were digitized and processed by a crystallographic method. After optimization of parameters for the image processing, the locally aver aged images revealed that each 2D crystal contained heterogeneous molecules . Single particle analysis was therefore applied to the 2D crystal images t o select homogeneous molecule images, and averaging the selected images sig nificantly improved map quality. Five major peak densities were clearly res olved in the new projection map, while two were found previously.