The Hemoprotein reference article from the English Wikipedia on 24-Apr-2004
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Hemoprotein

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A hemoprotein, or heme protein, is a protein containing a heme prosthetic group, either covalently or noncovalently bound to the protein itself. The iron in the heme is capable of undergoing oxidation and reduction (usually to +2 and +3, though stabilized ferryl [Fe+4] compounds are well known in the peroxidases). Hemoproteins are found in such diverse roles as transport (hemoglobin, myoglobin, neuroglobin, cytoglobin and leghemoglobin), catalysis (peroxidases), active membrane transport (cytochromes), and electron transfer (cytochrome c).