protoporphyrin type III

pro·to·por·phy·rin type III

The principal protoporphyrin found in nature (one of 15 possible isomers), characterized by the presence of four methyl groups, two vinyl groups, and two propionic acid side chains; a porphyrin derivative that, with iron, forms the heme of hemoglobin and the prosthetic groups of myoglobin, catalase, cytochromes, etc.
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