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, iron is bound to \nSelect and explain. \nA. Histidine, B. Leucine, C. Isoleucine, D. Valine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The iron atom of hemoglobin has six coordinated bonds : (i) Four bonds are formed between the iron and nitrogen atoms of porphyrin ring system; (ii) Fifth bond is formed between the nitrogen of histidine (proximal histidine: HisF8) of globin; and (iii) Sixth bond is formed with oxygen.', 'role': 'assistant'}]