the tritiated cardiotonic steroids , ouabain , digitoxin , and digitoxigenin are shown to photolabel the large polypeptide but not the glycoprotein or proteolipid component of the ( na+ + k+ ) -atpase when they are bound to the inhibitory site and exposed to light of 220 or 254 nm .
C0012258
digitoxin
C0012257
digitoxigenin