Which of the Following Statements Concerning Receptor Enzymes Is Correct

Which of the following statements concerning receptor enzymes is correct?

A) They are not usually membrane-associated proteins.
B) They contain an enzyme activity that acts on a cytosolic substrate.
C) They contain an enzyme activity that acts on the extracellular ligand.
D) They have a ligand-binding site on the cytosolic side of the membrane.
E) They have an active site on the extracellular side of the membrane.