The distribution of C12E8-solubilized oligomers of the (Na+ + K+)-ATPase

Gel filtration of (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.8) solubilized in octaethyleneglycol dodecylmonother ( C12E8 ) has been performed under conditions where active (alpha beta)2 dimers (Mr 265000) are obtained, and under conditions where dissociation into alpha beta monomers occurs without appreciable loss of activity. It is shown that the alpha beta monomers aggregate with time to form (alpha beta)2 dimers at low detergent concentrations with no change in enzymatic activity. At high detergent concentrations the aggregation is much slower, but the enzymatic activity is lost rapidly. Polyacrylamide gel electrophoresis in the presence of C12E8 also suggest that high concentrations of detergent dissociate the (alpha beta)2 dimer into smaller particles, and conditions for gel electrophoresis are described. The inactivating effect of C12E8 at high C12E8 /protein ratios can be related to a delipidation of the enzyme, with about 0.19 mg phospholipid required per mg protein for optimal activity. The experiments suggest that the solubilized (Na+ + K+)-ATPase can be disrupted into particles containing only one alpha-chain and one or two beta-chains without irreversible loss of activity, and that the stable form of the enzyme is an (alpha beta)2 dimer.