Ouabain, an Effective Inhibitor of Na⁺, K⁺-ATPase, Exhibits All of the Following

Ouabain, an effective inhibitor of Na⁺, K⁺-ATPase, exhibits all of the following characteristics EXCEPT:

A) It has a basic steroid structure.
B) It contains an unsaturated lactone ring at C-17.
C) It binds on the extracellular surface of Na⁺, K⁺-ATPase.
D) It binds tightly to the enzyme/ATP complex in producing the inhibition.
E) It is a cardiac glycoside.