heme

1. The porphyrin chelate of iron in which the iron is Fe(II) (or Fe²⁺); the oxygen-carrying, color-furnishing, prosthetic group of hemoglobin. 2. Iron complexed with nonporphyrins but related tetrapyrrole structures ( e.g., biliverdin h.). 3. Iron chelated with any porphyrin, irrespective of the valence state of the iron atom. SYN: ferroheme, ferroprotoporphyrin, reduced hematin. [G. haima, blood]

- h. a a derivative of h. found in cytochrome aa₃.

- h. c a derivative of h. found in cytochromes c, b₄, and f.

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heme or chiefly Brit haem 'hēm n the deep red iron-containing prosthetic group C₃₄H₃₂N₄O₄Fe of hemoglobin and myoglobin that is a ferrous derivative of protoporphyrin and readily oxidizes to hematin or hemin called also protoheme

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(hēm) 1. any quadridentate chelate of iron with the four pyrrole groups of a porphyrin, further distinguished as ferroheme or ferriheme referring to the chelates of Fe(II) and Fe(III) respectively. The four porphyrin ligands form a square-planar complex; the fifth and sixth coordination positions of the iron atom are perpendicular to the plane of the porphyrin and both may be occupied by strong field ligands, such as a nitrogen atom of a histidine residue of a protein, as in cytochromes, or only one may be so occupied, as in hemoglobin where the sixth position reversibly binds oxygen. 2. ferroheme. 3. protoheme IX, the heme of hemoglobin. See protoheme.