Specific Cu2+-catalyzed oxidative cleavage of Na,K-ATPase at the extracellular surface

Abstract

This paper describes specific Cu2+-catalyzed oxidative cleavage of alpha and beta subunits of Na,K-ATPase at the extracellular surface. Incubation of right side-out renal microsomal vesicles with Cu2+ ions, ascorbate, and H2O2 produces two major cleavages of the alpha subunit within the extracellular loop between trans-membrane segments M7 and M8 and L7/8. Minor cleavages are also detected in loops L9/10 and L5/6. In the beta subunit two cleavages are detected, one before the first S-S bridge and the other between the second and third S-S bridges. Na,K-ATPase and Rb+ occlusion are inactivated after incubation with Cu2+/ascorbate/H2O2. These observations are suggestive of a site-specific mechanism involving cleavage of peptide bonds close to a bound Cu2+ ion. This mechanism allows several inferences on subunit interactions and spatial organization. The two cleavage sites in L7/8 of the alpha subunit and two cleavage sites of the beta subunit identify interacting segments of the subunits. L7/8 is also close to L9/10 and to cation occlusion sites. Comparison of the locations of Cu2+-catalyzed cleavages with Fe2+-catalyzed cleavages (Goldshleger, R., and Karlish, S. J. D. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 9596-9601) suggests division of the membrane sector into two domains comprising M1-M6 and M7-M10/Mbeta, respectively.