27.
Which of the following statements concerning hemoglobin is correct?
(A) Oxygen binds to the porphyrin ligands of the heme groups.
(B) Carbon monoxide is toxic because it degrades the heme groups in hemoglobin.
(C) The four heme subunits of hemoglobin exhibit cooperativity in their binding of oxygen.
(D) The binding of oxygen by hemoglobin is pH insensitive.
(E) Hemoglobin binds O2 irreversibly.