Determination of the distribution of sodium and potassium ion activated adenosinetriphosphatase among the various oligomers formed in solutions of nonionic detergents.

Sodium and potassium ion activated adenosinetriphosphatase [(Na+ + K+)-ATPase] can be dispersed from the membrane-bound state, with the stable retention of the capacity to display (Na+ + K+)-ATPase activity, by treatment with solutions of a homogeneous, nonionic detergent, octaethylene glycol dodecyl ether. The dispersed enzyme is incapable of turnover, however, in solutions where the free detergent concentration is above the critical micelle concentration. Treatment of solutions of this enzyme with the crosslinking reagent glutaraldehyde results in the quantitative, covalent coupling of the alpha-and beta-polypeptides. The various covalent products formed, when visualized on sodium dodecyl sulfate-polyacrylamide gels, are integral oligomers of the asymmetric unit (alpha beta) of the enzyme. The noncovalent oligomers from which these products are derived can be separated on sucrose gradients based on differences in their respective sedimentation coefficients, but these sedimentation coefficients are highly dependent on the concentration of detergent in the gradient. Furthermore, the cross-linking assay reveals that changes in the aggregation state of the enzyme occur as detergent:protein ratios are varied or when the enzyme is added to the ATPase assay. These observations suggest that earlier conclusions about the oligomers of this enzyme present in detergent solution were significantly in error.