Two-dimensional arrays of membrane-bound (Na⁺, K⁺) - ATPase

Abstract

(Na+, K+) - ATPase is a trans-membrane protein which utilizes energy from ATP hydrolysis to transport K+ into the cell and Na+ out of the cell against the concentration gradient of both of these ions. It consists of a catalytic subunit (α, M.W. 100,000) and a glycoprotein chain (β, M.W. 40,000). It is however, uncertain if the B structure or an oligomeric (αβ)2 structure forms the minimum active unit. The sequence information on the α and β-subunits is also incomplete. Therefore information about the structure of the enzyme should prove helpful in answering some of the outstanding questions about its function.(Na+, K+) - ATPase was purified in membrane-bound form from the outer medulla of pig and dog kidneys according to the procedure of P.L. Jorgensen. The activity measurements and polyacrylamide gel electrophoresis indicated that the preparations were 75-85% pure.

Structure of (Na+,K+)-ATPase as revealed by electron microscopy and image processing.

“…The former had been employed previously (21) where it induced crystals over a period of 4-6 wk . The crystallization time can be reduced to 2-6 d by using Na3VO4 (ortho) (18). Crystallization took considerably longer (>7 wk in some cases) with K2HPO4 and K3CrO4, and was neither as reproducible nor as extensive as with the vanadate salts .…”