An Example of Protein Structure

The peptide backbone and the heme group are shown overlain on the space-filling model. The helical segments are designated by the letters A through H. The terms NHg and COO indicate the N-terminal and C-terminal ends, respectively. 

Why does oxygen have imperfect binding to the heme group  

In the absence of the protein, the iron of the heme group can be oxidized to Fe(III) the oxidized heme will not bind oxygen. Thus, the combination of both heme and protein is needed to bind O2 for oxygen storage. 

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