This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'In hemoglobin, the innate affinity of heme for carbon monoxide is diminished by the presence of - \nSelect and explain. \nA. His F8, B. His E7, C. Gly B6, D. Thr C4', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Isolated heme binds carbon monoxide (CO) 25,000 times more strongly than oxygen. However, in myoglobin and hemoglobin, heme binds carbon monoxide to only about 200 times more strongly than oxygen.\nThis is because of distal histidine (His E7 of protein part of hemoglobin and myoglobin create a hindered environment which precludes the high-affinity orientation of CO.\nThe details of this mechanism are not required at this level.', 'role': 'assistant'}]