Sodium-potassium-activated adenosine triphosphatase. IV. Characterization of the phosphoprotein formed from orthophosphate in the presence of ouabain.

Microsomes prepared from electric organ of Electrophorus electricus or cat brain and exposed to ouabain will react with orthophosphate to form a phosphorylated protein. The electrophoretic mobilities of the phosphopeptides cleaved by peptic and Pronase digestion of the microsomes after interaction with phosphate are indistinguishable from those previously known to be formed from microsomes and ATP. The chemical stability of the bound phosphate is also similar to that of the phosphate formed from ATP. N-Ethylmaleimide treatment does not prevent ouabain binding, but does prevent the subsequent incorporation of orthophosphate.