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Structure of heme b

Heme b is the most abundant heme. Hemoglobin and myoglobin are oxygen transport proteins that contain heme B. The iron ion in heme B is bound to the four nitrogens of the heterocyclic porphyrin ring (forming a plane). The reversible bonding with oxygen is why hemoglobin is so useful for transporting oxygen around the body. Oxygen binds in an "end-on bent" geometry where one oxygen atom binds to iron (Fe), and the other protrudes at an angle. (Figure by Yikrazuul on August 3, 2010. Public domain.)

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