Myoglobin temperature dependence

A similar study was performed on ruthenium-modified myoglobins, in which AG variations were obtained by changing the nature of the ruthenium complex covalently bound to the protein, and by substituting a porphyrin to the heme [137]. It is gratifying to observe that, in spite of the rather heterogeneous character of this series, the study leads to an estimation of 1.9 to 2.4 eV for A which is consistent with the value 2.3 eV derived in section 3.2.1 from temperature dependent experiments. Satisfactory agreement between the results given by the two methods is also observed in the case of ruthenium-modified cytochrome c [138]. 

A variety of physical methods has been used to ascertain whether or not surface ruthenation alters the structure of a protein. UV-vis, CD, EPR, and resonance Raman spectroscopies have demonstrated that myoglobin [14, 18], cytochrome c [5, 16, 19, 21], and azurin [13] are not perturbed structurally by the attachment of a ruthenium complex to a surface histidine. The reduction potential of the metal redox center of a protein and its temperature dependence are indicators of protein structure as well. Cyclic voltammetry [5, 13], differential pulse polarography [14,21], and spectroelectrochemistry [12,14,22] are commonly used for the determination of the ruthenium and protein redox center potentials in modified proteins. 

K for myoglobin (Parak et al., 1981). Thus, measurements of (x ) at temperatures below this value should show a much less steep temperature dependence than measurements above, if nonharmonic or collective motions (whose mean-square displacement is denoted (x )c) are a significant component of the total (x ). Figure 21 illustrates the expected behavior of (x )v, x, and their sum for a simple model system in which a small number of substates are separated by relatively large barriers. In practice, the relative contributions of simple harmonic vibrations and coUective modes will vary from residue to residue within a given protein. 

Taken together with the temperature dependence of the x ) values, this study of the thermal expansion of myoglobin provides the most detailed picture yet available of the physical chemistry of a protein. It... 

Four spin-labelled derivatives of sperm whale metmyoglobin were prepared by site-directed mutagenesis.101 Cyanide anion or imidazole was added to prepare low-spin Fe(III). Iron relaxation rates were measured by saturation recovery or inversion recovery between 5 and 17 K and by analysis of the temperature-dependent contribution to the CW line widths of the iron signal at 20 to 160 K. The nitroxyl 7i values in spin-labelled Zn-substituted myoglobin were measured to provide values in the absence of interaction with the more rapidly-relaxing Fe(III). The full shapes of the nitroxyl saturation-recovery curves for the spin-... 

Figure 16.12 The temperature-dependent behavior of the denaturation enthalpy and entropy of ribonuclease (RNase) and myoglobin (Mb) under the assumption that AjjjCp is constant (dashed line) or decreasing with increasing temperature (solid line). Reproduced with permission from P. L. Privalov, Ann. Rev. Biophys. Chem. 18, 47 (1989). 1989, by Annual Reviews http //www.AnnualReviews.org...

Fig. 2. Temperature dependence of the partial specific heat capacity for pancreatic ribonuclease A (RNase), hen egg-white lysozyme (Lys), sperm whale myoglobin (Mb), and catalase from Thermus thermophilus (CTT). The flattened curves are for RNase and Lys with disrupted disulfide cross-links and for apomyoglobin, when polypeptide chains have a random coil conformation without noticeable residual structure (Privalov et al., 1988).

Fig. 4. Temperature dependence of the specific enthalpy of denaturation of myoglobin and ribonuclease A (per mole of amino acid residues) in solutions with pH and buffer providing maximal stability of these proteins and compensation of heat effects of ionization (see Privalov and Khechinashvili, 1974). The broken extension of the solid lines represents a region that is less certain due to uncertainty in the A°CP function (see Fig. 2). The dot-and-dash lines represent the functions calculated with the assumption that the denaturation heat capacity increment is temperature independent.

The temperature dependence of the kinetics of myoglobin has been studied using cyclic voltammetry. These experiments were conducted over a range of temperatures (10-50 °C) to determine the change in reaction center entropy... 

Vibrational echo experiments have also been applied to the CO-stretching mode of myoglobin-CO, mutant myoglobins, and hemoglobin-CO. Temperature-dependent vibrational echo and lifetime measurements have been performed on CO bound to the active site of native Mb in a variety of solvents and two mutants of myoglobin and HbCO in the same solvent as a Mb study. In addition, an isothermal (300 K) viscosity dependence of MbCO has been recorded. 

Figure 4.2. Temperature dependence of the rate constant of electron transfer (Icet) in myoglobin modified covalently by donor-acceptor groups (a) and the deviation of various dynamic quantities from normal harmonic behaviour obtained by molecular dynamic simulation, inelastic neutron scattering, MOssbauer spectroscopy and spectral broadening analysis (b). (Likhtenshtein et al., 2000). Reproduced with permission.

P.-C. Lin, U. Kreutzer, and T. Jue. Anisotropy and temperature dependence of myoglobin translational diffusion in myocardium implication for oxygen transport and cellular architecture../. Am. Chem. Soc., 56 658-666, 1934. 

Other measurements also suggest that the hydration water of myoglobin and the internal motions of the protein are coupled. For example, the 10 GHz dielectric response of the water of myoglobin crystals has a temperature dependence close to that of the heme iron (Singh et al., 1981). The O-D stretching band (Doster et al, 1986) is also correlated with the above properties (Fig. 26). The temperature dependence of the infrared properties and of the heat capacity (Doster et al., 1986) were interpreted as indicating that the hydration water melts at 190 K and... 

Fig. 26. Temperature dependence of various properties of myoglobin crystals , frequency of the O-D band maximum (IR) —, dielectric relaxation time of water (schematic) ---—, Lamb-Mossbauer factor,/o, after subtracting the harmonic mode (sche-...

The protein properties include (1) motions of several proteins monitored by ESR spin labels (Belonogova et al., 1978, 1979 Likhtenshtein, 1976 Steinhoff et al., 1989) and Mossbauer labels (Belonogova et al., 1979 Likhtenshtein, 1976) (2) temperature dependence of neutron scattering for myoglobin (Cusack, 1989 Doster et al., 1989) (3) Mossbauer spectra (Parak et al., 1988) and RSMR spectra (Goldanskii and Krupyanskii, 1989) of myoglobin and (4) mechanical properties of lysozyme crystals (Morozov and Gevorkyan, 1985 Morozov et al., 1988). 

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