Heme groups myoglobin

Fraunfelder and co-workers [65-68] have found the same relationship in the reduction kinetics of CO and O2 ligand coordination bonds with the complex-forming Fe ions of the heme group myoglobin upon photodissociation of these bonds induced by laser photolysis of 10 s duration. The formation of Fe-CO and Fe-02 bonds after photolysis was registered with a spectrophotometer by restoration of the mother compound absorption spectrum in the wide range of times (10 -10 s) and temperatures (2-300 K). Before photolysis the six-coordinate Fe ion is in the heme plane. The coordination bond break causes not only the ligand shift but also... 

Figure 24.11 A shows a schematic structure of myoglobin, a protein that contains one heme group. Myoglobin is a globular protein, one that folds into a compact, roughly spherical shape. Globular proteins are generally soluble in water and are mobile within cells. Myoglobin is found in the cells of skeletal muscle.

We assume in the following that the ligand is bound in a binding pocket of depth 6 —a = 7 A involving a potential barrier AU = 25 kcal/mol, similar to that of streptavidin (Chilcotti et al., 1995). We also assume that the diffusion coefficient of the ligand is similar to the diffusion coefficient of the heme group in myoglobin (Z) = 1 A /ns) as determined from Mofibauer spectra (Nadler and Schulten, 1984). 

FIGURE 15.26 Oxygen and carbon monoxide binding to the heme group of myoglobin. 

Cytochromes were first named and classified on the basis of their absorption spectra (Figure 21.9), which depend upon the structure and environment of their heme groups. The b cytochromes contain iron—protoporphyrin IX (Figure 21.10), the same heme found in hemoglobin and myoglobin. The c cytochromes contain heme c, derived from iron-protoporphyrin IX by the covalent attachment of cysteine residues from the associated protein. UQ-cyt c... 

Imately 65 X 55 X 50 It Is composed of four polypeptide chains each resembling quite closely the myoglobin chain The three dimensional structure of the subunits Is held together by weak noncovalent bonds The polar amino acid side chains are In contact with the solvent, and the nonpolar residues are located In the Interior of the molecule or In regions which form the contacts between chains The heme group Is located In a pocket In each chain residues In contact with heme are Invariable ( e are the same In different mammalian hemoglobins) and the bonds between heme and chain are hydrophobic Interactions Contacts between like chains (a-a are... 

The biochemical activity and accessibility of biomolecule-intercalated AMP clays to small molecules was retained in the hybrid nanocomposites. For example, the absorption spectrum of the intercalated Mb-AMP nanocomposite showed a characteristic soret band at 408 nm associated with the intact prosthetic heme group of the oxidised protein (Fe(III), met-myoglobin) (Figure 8.9). Treatment of Mb with sodium dithionite solution resulted in a red shift of the soret band from 408 to 427 nm, consistent with the formation of intercalated deoxy-Mb. Reversible binding of CO under argon to the deoxy-Mb-AMP lamellar nanocomposite was demonstrated by a shift in the soret band from 427 to 422 nm. Subsequent dissociation of CO from the heme centre due to competitive 02 binding shifted the soret band to 416nm on formation of intercalated oxy-Mb. 

Each of the subunits, a and P (as well as the closely related myoglobin molecule), has a prosthetic heme group to which the oxygen molecule binds. There are no covalent bonds between the subunits of Hb. The aggregate is maintained by a combination of weak direct subunit-subunit interactions as well as by indirect interactions mediated by the solvent. 

---