Myoglobin forms

Compared with Molsidomine, both SIN-1 and SIN-1A are reported to induce similar, but more rapid hypotensive action [95, 96]. SIN-1A, after undergoing oxidation in the presence of oxygen or, in vivo, possibly by redox-active enzymes such as cytochrome C [97, 98] or by reaction with ferric myoglobin formed during reperfusion injury [99], releases NO through an intermediate radical cation. 

Fandrich, M., Forge, V., Buder, K., Kittler, M., Dobson, C. M., and Diekmann, S. (2003). Myoglobin forms amyloid fibrils by association of unfolded polypeptide segments. Proc. Natl. Acad. Sci. USA 100, 15463-15468. 

Yonetoni and co-workers (1972) have shown that hemoglobin and myoglobin form nitrosyl complexes with different bond angles at 77 K and at room temperature. The high-temperature species has less g tensor anisotropy (g = 2.03, gy = 1.98-1.99) and poorly resolved hyperfine splitting. Addition of glycerol at high concentrations prevented the transition between these forms. 

In general, percent metmyoglobin is reported and not percent deoxy- or percent oxymyo-globin. Formulas for the two ferrous myoglobin forms can be obtained from Krzywicki (1982). 

The heme pocket. The helices of hemoglobin (and myoglobin) form a hydrophobic pocket for the heme and provide an environment where the iron atom reversibly binds oxygen. The chemical structure of heme is shown in figure 5.10 and is described in atomic detail in chapters 10 and 14. (Illustration copyright by Irving Geis. Reprinted by permission.)... 

Fig. 8. MCD spectra of ferryl iron. Low-temperature (50 or 100K) MCD spectra of ferryl iron in different proteins HRPCII, horse-radish peroxidase compound II HRPCX, horse-radish peroxidase compound X YCCP, yeast cytochrome c peroxidase compound I PsCCP, compound I of the dihaem cytochrome c peroxidase from Pseudomonas aeruginosa-, Mb pH 3.5, ferryl myoglobin formed at pH 3.5 MbpD9.0, the same compound found at pD9.0. Note the similarity of all the spectra with the exception of the alkaline form of ferryl myoglobin. Reprinted with permission from Cheesman, M.R., Greenwood, C. and Thomson, A.J. (1991) Adv. Inorg. Chem. 36, 201-255.

Jensen and Urbain, 1936a Jensen, 1945 Niven et al., 1949 Niven, 1951). Methemoglobin and metmyoglobin, as well as hemoglobin and myoglobin, form unstable addition compounds with hydrogen peroxide, which then decompose with destruction of the heme nucleus (Keilin and Hartree, 1950). 

Figure 2.1 Kendrew s model of the low-resolution structure of myoglobin shown in three different views. The sausage-shaped regions represent a helices, which are arranged in a seemingly Irregular manner to form a compact globular molecule. (Courtesy of J.C. Kendrew.)...

Since there are so few direct packing interactions between protein molecules in a crystal, small changes in, for example, the pH of the solution can cause the molecules to pack in different ways to produce different crystal forms. The structures of some protein molecules such as lysozyme and myoglobin have been determined in different crystal forms and found to be essentially similar, except for a few side chains involved in packing interactions. Because they are so few, these interactions between protein molecules in a crystal do not change the overall structure of the protein. However,... 

The secondary and tertiary structures of myoglobin and ribonuclease A illustrate the importance of packing in tertiary structures. Secondary structures pack closely to one another and also intercalate with (insert between) extended polypeptide chains. If the sum of the van der Waals volumes of a protein s constituent amino acids is divided by the volume occupied by the protein, packing densities of 0.72 to 0.77 are typically obtained. This means that, even with close packing, approximately 25% of the total volume of a protein is not occupied by protein atoms. Nearly all of this space is in the form of very small cavities. Cavities the size of water molecules or larger do occasionally occur, but they make up only a small fraction of the total protein volume. It is likely that such cavities provide flexibility for proteins and facilitate conformation changes and a wide range of protein dynamics (discussed later). 

In this form, Alhas the units of torr.) The relationship defined by Equation (A15.4) plots as a hyperbola. That is, the MbOg saturation curve resembles an enzyme substrate saturation curve. For myoglobin, a partial pressure of 1 torr for jbOg is sufficient for half-saturation (Figure A15.1). We can define as the partial pressure of Og at which 50% of the myoglobin molecules have a molecule of Og bound (that is, F= 0.5), then... 

During the curing process, some of the nitrites are converted to nitric oxide. This combines with the myoglobin proteins in the muscle of the meat to form the deep red nitric oxide myoglobin, which causes cured meats such as ham to turn pink during the smoking process. 

Sodium nitrate has been used for centuries to cure meat. Bacterial action during curing converts the sodium nitrate into sodium nitrite, which kills the bacteria that cause botulism, and combines with the myoglobin in the meat to form the pink color associated with ham. 

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