Prostaglandin E2 synthase
Na,K-ATPase is responsible for transport of Na+- and K+-ions across plasma membranes in order to keep concentration gradients of these ions between the interior and exterior of cells.
Purified Na,K-ATPase can be purified in native membranes. The small size of these crystals introduces problems not normally encountered for large and well-ordered 2-D crystals. The signal-to-noise ratio from each individual crystal will be comparatively low but this can be compensated for by analysis of a large number of crystals. Furthermore, the orientation of the crystal and thus the projection direction is less certain and has to be checked carefully throughout the image processing. By considering those concepts we have been able to determine the structure of Na,K-ATPase at 9.5 Å resolution. From this map it is possible to localize the subunits, to find the positions of the functionally and structurally characteristic domains of the catalytic alpha-subunit, and to determine approximate positions of the transmembrane helices. Interesting comparisons can be made with the atomic models of Ca2+-ATPase which has a similar catalytic subunit but lacks the other two subunits present in renal Na,K-ATPase. The most striking difference is the large inter-domain movements in the catalytic subunit that must take place during the pump process.
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