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  • 1
    Electronic Resource
    Electronic Resource
    Low temperature optical absorption spectroscopy: an approach to the study of stereodynamic properties of hemeproteins (1995)
    Springer
    European biophysics journal 23 (1995), S. 385-398 
    Details
    ISSN: 1432-1017
    Keywords: Protein dynamics ; Vibrational coupling ; Anharmonic motions ; Conformational substates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract In this short review we show how suitable analysis of the temperature dependence of the optical absorption spectra of metalloproteins can give insight into their stereodynamic properties in the region of the chromophore. To this end, the theory of coupling between an intense allowed electronic transition of a chromophore and Franck-Condon active vibrations of the nearby atoms is applied to the Soret band of hemeproteins to obtain an analytical expression suitable for fitting the spectral profile at various temperatures. The reported approach enables one to separate the various contributions to the overall bandwidth together with the parameters that characterize the vibrational coupling. The thermal behavior of these quantities gives information on the dynamic properties of the active site and on their dependence upon protein structure and ligation state. The Soret band of hemeproteins appears to be coupled to high frequency vibrational modes of the heme group (as already shown by resonance Raman spectroscopy) and to a “bath” of low frequency modes most likely deriving from the bulk of the protein. For the deoxy derivatives inhomogeneous broadening arising from conformational heterogeneity appears to contribute substantially to the linewidth. The data indicate the onset; at temperatures near 180 K, of large scale anharmonic motions that can be attributed to jumping among different conformational substates of the protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196825
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  • 2
    Electronic Resource
    Electronic Resource
    Low temperature optical spectroscopy of cobalt-substituted hemocyanin from Carcinus maenas (1993)
    Springer
    European biophysics journal 22 (1993), S. 157-167 
    Details
    ISSN: 1432-1017
    Keywords: Hemocyanin ; Optical spectra ; Vibrational coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract In this work we report the optical absorption spectra of three cobalt-substituted derivatives of hemocyanin (He) from Carcinus maenas, in the temperature range 300–20 K. The derivatives studied are the mononuclear (Co2+)-He with a single cobalt ion in the “CuA” site, the binuclear (Co2+)2-He and the binuclear mixed metal (Co2+-Cu1+)-He. At low temperature three main bands are clearly resolved; the temperature dependence of their zeroth, first and second moments sheds light on the stereodynamic properties in the surroundings of the chromophore. Within the limits of the reported analysis, in the binuclear derivatives the motions coupled to the chromophore appear to be “essentially harmonic” in the whole temperature range investigated; moreover the data are consistent with the presence of an exogenous ligand strongly bound to the two metal ions. For the mononuclear derivative an “essentially harmonic” behavior is evident only up to 200 K where the data are consistent with the presence of an exogenous ligand much less strongly bound, while at higher temperatures the behavior of the spectra indicates the onset of very large anharmonic contributions to motions, that plausibly involve the above exogenous ligand and, quite likely, the entire active site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00185776
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  • 3
    Electronic Resource
    Electronic Resource
    Low temperature optical spectroscopy of low-spin ferric hemeproteins (1996)
    Springer
    European biophysics journal 24 (1996), S. 117-124 
    Details
    ISSN: 1432-1017
    Keywords: Protein dynamics ; Optical spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We report the Soret absorption spectra (500-350 nm) of the cyanomet derivatives of human hemoglobin and horse myoglobin, in the temperature range 300-20 K and in two different solvents (65% v/v glycerol-water or 65% v/v ethylene glycol-water). In order to obtain information on stereodynamic properties of active site of the two hemeproteins, we perform an analysis of the band profiles within the framework of electron-vibrations coupling. This approach enables us to single out the various contributions to the spectral bandwidth, such as those arising from non-radiative decay of the excited electronic state (homogeneous broadening) and from the coupling of the electronic transition i) with high frequency modes (that determines the vibronic structure of the band) and ii) with a “bath” of low frequency modes (that is responsible for the temperature dependence of the experimental spectra). We discuss the relevant parameters and their temperature dependence and compare them with the ones already reported for other derivatives of the same hemeproteins in the same solvents. In particular, non-harmonic contributions to soft modes are found, for cyanomet derivatives, to be larger than those observed for liganded carbonmonoxy but smaller than those observed for unliganded deoxy derivatives. The reported data enable us to obtain information on the dependence of stereodynamic properties of the heme pocket upon iron oxidation state, dimensions of the exogenous ligand and composition of the external matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00180268
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal broadening of the Soret band in heme complexes and in heme-proteins: role of iron dynamics (1994)
    Springer
    European biophysics journal 23 (1994), S. 349-352 
    Details
    ISSN: 1432-1017
    Keywords: Protein dynamics ; Optical spectroscopy ; Protoporphyrin IX
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We report the thermal broadening of the Soret band in heme-CO, heme-OH and protoporphyrin IX in the temperature range 300–20 K. For protoporphyrin IX the temperature dependent Gaussian line broadening follows the behavior predicted by the harmonic approximation in the entire temperature range investigated. In contrast, for heme-CO and heme-OH the harmonic behavior is obeyed only up to about 180 K and an anomalous line broadening increase is observed at higher temperatures. This effect is attributed to the onset of anharmonic motions of the iron atom with respect to the porphyrin plane. Comparison with previously reported analogous data for heme proteins enables us to suggest that the onset of substate interconversions in these latter systems can be reflected in motions of the iron atom with respect to the porphyrin plane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188658
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  • 5
    Electronic Resource
    Electronic Resource
    Stabilization of the monoolein Pn3m cubic structure on trehalose glasses (1999)
    Springer
    European biophysics journal 28 (1999), S. 294-301 
    Details
    ISSN: 1432-1017
    Keywords: Key words Lipid polymorphism ; Cubic phases ; X-ray diffraction ; Dehydration stress ; Trehalose protective function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Trehalose is known to protect some organisms from various stresses due to drought and high temperature. To explore the molecular mechanism of the protective function, the mesomorphic properties of the monoolein-water system, dried in the presence of trehalose, were studied by X-ray diffraction. While, in pure water, two bicontinuous inverse cubic structures (the Pn3m and Ia3d phases) and a lamellar Lα phase exist as a function of concentration, only the Pn3m cubic phase has been detected in concentrated trehalose solutions or in trehalose glasses, even under extremely dry conditions. Depending on the sugar concentration, or after glass dehydration, the Pn3m cubic unit cell decreases to very low values, much below the smaller one observed in pure water. However, as no phase transitions occur, a simple osmotic mechanism can be excluded. An additional stabilization of the lipid phase, arising from interfacial free energy changes due to trehalose-water-lipid direct interactions, and large enough to affect the energetic balance between the Pn3m and the Ia3d cubic phases, evidently occurs. Moreover, no differences in the Pn3m cubic structure were observed when the sugar platelets convert to the glassy state; no apparent structural modifications that can be related to mechanical pressure exerted on the lipid phase have been detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490050211
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamic properties of the active site of azurin studied by the temperature dependence of the optical spectrum (1990)
    Springer
    BioMetals 3 (1990), S. 77-79 
    Details
    ISSN: 1572-8773
    Keywords: Azurin ; Blue copper proteins ; Optical spectroscopy at cryogenic temperatures ; Protein dynamics ; Charge transfer transitions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We report the optical absorption spectra of azurin (Pseudomonas aeruginosa) in the temperature range 290-20 K. The samples used are protein aqueous solutions containing 65% (by Vol.) glycerol as cryoprotectant. The measured spectra are deconvoluted in gaussian components and the temperature dependence of the zeroth, first and second moment of the observed bands is analyzed using the harmonic Franck-Condon approximation for the coupling between electronic transitions and nuclear vibrations. The analysis provides information on the stereodynamic properties of the active site of this protein. The possible functional relevance of these results is also suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01179507
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of some monohydric alcohols on the functional stability of bovine liver β-galactosidase (1979)
    New York : Wiley-Blackwell
    Biopolymers 18 (1979), S. 1965-1974 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report on experiments showing that the presence of some monohydric alcohols in the solution medium perturbs the kinetics of bovine liver β-galactosidase. The effect increases with increasing alcohol concentration and alkyl group size. To explain this effect we suggest a model that considers the existence of functional and nonfunctional enzyme conformations in thermodynamical equilibrium. This equilibrium is dependent both on alcohol concentration and on alkyl group size.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1979.360180810
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of some monohydric alcohols on the oxygen affinity of hemoglobin: Relevance of solvent dielectric constant and hydrophobicity (1979)
    New York : Wiley-Blackwell
    Biopolymers 18 (1979), S. 1975-1988 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the effect of methanol, ethanol, iso-propanol, and n-propanol on the reaction of hemoglobin with oxygen. The oxygen affinity was found to decrease with increasing alcohol concentration and alkyl group size; no detectable effect on Hill's constant was found. Difference spectroscopy indicated KR not to be affected by the presence of alcohols; the lowered affinity was then attributed to an altered equilibrium between T and R conformations of hemoglobin. The results have been analyzed in such a way as to allow separation of electrostatic contributions to free energy difference between the T and R states from nonelectrostatic ones. The nonelectrostatic term has been attributed to protein-solvent hydrophobic interactions. Values of hydrophobic free energy are in good agreement with analogous data estimated by correlating different results previously reported in the literature.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1979.360180811
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  • 9
    Electronic Resource
    Electronic Resource
    Structural and dynamic properties of the heme pocket in myoglobin probed by optical spectroscopy (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1977-1997 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report the optical absorption spectra of sperm whale deoxy-, oxy-, and carbonmonoxymyoglobin in the temperature range 300-20 K and in 65% glycerol or ethylene glycol-water mixtures. By lowering the temperature, all bands exhibit half-width narrowing and peak frequency shift; moreover, the near-ir bands of deoxymyoglobin show a marked increase of the integrated intensities. Opposed to what has already been reported for human hemoglobin, the temperature dependence of the first moment of the investigated bands does not follow the behavior predicted by the harmonic Franck-Condon approximation and is sizably affected by the solvent composition; this solvent effect is larger in liganded than in nonliganded myoglobin. However, for all the observed bands the behavior of the second moment can be quite well rationalized in terms of the harmonic Franck-Condon approximation and is not dependent on solvent composition. On the basis of these data we put forward some suggestions concerning the structural and dynamic properties of the heme pocket in myoglobin and their dependence upon solvent composition. We also discuss the different behaviors of myoglobin and hemoglobin in terms of the different heme pocket structures and deformabilities of the two proteins.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360271209
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamic properties of oxy- and carbonmonoxyhemoglobin probed by optical spectroscopy in the temperature range of 300-20 K (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 1769-1779 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have studied the absorption bands of oxy- and carbonmonoxyhemoglobin in the wavelength range of 650-350 nm (visible and Soret bands) and in the temperature range of 300-20 K. The spectra in the whole temperature range have been successfully deconvoluted in terms of gaussian components. The analysis of the temperature dependence of the first and second moment of the bands enables us to compare dynamic properties of the heme group in oxy- and carbonmonoxyhemoglobin. The results of the analysis indicate that the “mean-effective” frequency of the nuclear motion coupled to the electronic transition responsible for the visible bands is higher in carbonmonoxy- than in oxyhemoglobin. The possible functional relevance of this finding is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360261009
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