STUDIES ON (NA++K+) ACTIVATED ATPASE .42. REVERSIBLE INACTIVATION OF (NA++K+)-ATPASE BY USE OF A CLEAVABLE BIFUNCTIONAL REAGENT

1. 1. Purified (Na+ + K+)-ATPase, prepared from rabbit kidney outer medulla, is incubated with the bifunctional NH2-directed reagent dimethyl 3,3′-dithiobispropionimidate. This results in a cross-link between the subunits of the enzyme and a simultaneous reduction of the (Na+ + K+)-ATPase and K+-stimulated p-nitrophenylphosphate activities. 2. 2. The most abundant cross-link product is a dimer of the two different subunits of the enzyme. 3. 3. Reduction of the disulfide cross-link by dithioerythritol results in partial recovery of the original subunit structure of the enzyme and of the (Na+ + K+)-ATPase and K+-stimulated p-nitrophenylphosphatase activities. 4. 4. These results suggest that a free mobility of the subunits of the (Na+ + K+)-ATPase system relative to each other is essential for proper functioning of both enzyme activities. © 1979.