Iron in myoglobin and

Figure 8.4. Iron protoporphyrin DC, the prosthetic group in myoglobin, and the coordination geometry of iron in myoglobin and oxymyoglobin.

The PDOS of the iron in deoxy- and CO-myoglobin and of myoglobin with different degrees of water content was also determined by Achterhold et al. [112, 113]. They found that the modes with an energy larger than 3 meV (24 cm ) are harmonic at physiologically relevant temperatures. Those below 3 meV exhibit a... 

Iron (Fe) is quantitatively the most important trace element (see p. 362). The human body contains 4-5 g iron, which is almost exclusively present in protein-bound form. Approximately three-quarters of the total amount is found in heme proteins (see pp. 106,192), mainly hemoglobin and myoglobin. About 1% of the iron is bound in iron-sulfur clusters (see p. 106), which function as cofactors in the respiratory chain, in photosynthesis, and in other redox chains. The remainder consists of iron in transport and storage proteins (transferrin, ferritin see B). 

For simplicity the iron-oxygen interaction in myoglobin and hemoglobin (but not hemerythnn) was discussed in terms of neutral oxygen molecules binding to Fe". However. much of the cuTent literature discusses these phenomena in terms of superoxo and peroxo complexes and one sees Fe,M-0 . Discuss what these formulations and tents mean, and describe the related consequences in terns of charges, electron spins, etc.113... 

Fig. 19.6 Close-up of the heme group in myoglobin and hemoglobin. Note that Ihe iron atom docs not lie in the plane of Ihe heme group.

Fig. 3. Axial ligands of the heme iron in hemoproteins. The imidazole ring of a histidyl residue is one of the axial ligands in myoglobin, hemoglobin, and cytochrome c. In native cytochrome c the sixth ligand is a methionyl residue of the polypeptide chain. In partially denatured cytochrome c, and in myoglobin and hemoglobin, a variety of ligands, some of which are shown in the figure, may bind to the sixth coordination site...

Figure 3 Simplified structure of the oxyheme imit in myoglobin and hemoglobin. There are two characteristic histidines in the heme pocket, proximal (F8) and distal (E7) histidines. The latter histidine strongly stabilizes the iron-boimd02 via hydrogen-bonding interaction...

In the synthetic iron porphyrin, O2 affinity mainly depends on the strengths of the <7-donation from the lone pair of O2 to the heme-iron dz orbital and 7r-back donation from the d/r orbital on the iron to the Jt orbital of 2. To evaluate the O2 affinity and/or O2 binding dynamics in myoglobin and hemoglobin, O2 - protein interaction is a further important factor. For example, the O2 dissociation rate constant for oxymyoglobin is relatively smaller than those of O2 complexes... 

One of the abnormal imidazole groups in myoglobin, and four of those in hemoglobin (one for each iron atom) are also nontitratable by virtue of a covalent bond to an iron atom, these being the imidazole groups by which the hemes are attached to the protein portions of the two molecules. In addition, these groups are buried and inaccessible to the solvent. 

---