In hemoglobin, the innate affinity of heme for carbon monoxide is diminished by the presence of :: (A) His F8, (B) His E7, (C) Gly B6, (D) Thr C4
Answer is B. The heme has high affinity for carbon monoxide (about 25000 more than for 02). But when heme molecule is associated with Histidine E 7 (as occurs in myoglobin), its affinity for CO is drastically reduced because His E 7 creates a hindered environment for CO by disturbing the orientation of atoms in heme molecules.