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A P Demchenko

Publications and source records attributed to A P Demchenko.

At least 37 records · Page 2Linked to original sources
PubMed1988

Temperature-dependent shift of fluorescence spectra without conformational changes in protein; studies of dipole relaxation in the melittin molecule.

When studying bee venom melittin in an ordered tetrameric form we found a shift of the fluorescence spectrum to a longer wavelength with a rise in temperature above 25 degrees C. The application of the methods of circular dichroism, temperature-perturbation difference spectrophotometry, gel filtration, ionic quenching and polarization of Trp-19 fluorescence argues against the possibility of dissociation and change in conformation with the rise in temperature. The spectral shifts are, probably, caused by dipole-orientational structural relaxation of the tryptophanyl environment in the excited state at nanosecond times. The dependence of the fluorescence spectrum on the excitation wavelength was found to be a function of temperature. This function was applied to determine the dipole-orientational relaxation times.

Algorithms↗
PubMed1988

Red-edge-excitation fluorescence spectroscopy of indole and tryptophan.

Studies on the dependence of indole and tryptophan fluorescence emission spectra on excitation wavelength, lambda ex, show that the emission shifts to longer wavelengths for red-edge excitation in different solid and viscous solvents. In solid systems the spectral shifts for excitation in the range from 290 to 310 nm can reach tens of nm, and they are more significant than changes of lambda ex. In a viscous medium the magnitude of this effect is shown to be directly related to the dipole-reorientational relaxation of solvent molecules in the environment of the chromophore, which allows the relaxation times to be estimated. The method involves simple steady-state measurements of fluorescence spectra at the maximum and at the red edge of the absorption band. Since it is not necessary to obtain information on the fluorescence spectra of completely relaxed states, this method for the estimation of relaxation times may have advantages in studies of proteins compared with the conventional relaxation shift method, and may produce complementary information to that obtained by nanosecond time-resolved spectroscopy.

Ethylene Glycol↗
PubMed1988

Red-edge-excitation fluorescence spectroscopy of single-tryptophan proteins.

With the aim of finding non-equilibrium dipole-relaxational electronic excited states of tryptophan residues in proteins the dependence of the fluorescence emission maximum on excitation wavelength was studied for several proteins containing a single tryptophan residue per molecule. Spectral shifts upon red-edge excitation are not observed for short wavelength-emitting proteins (azurin, two-calcium form of whiting parvalbumin, ribonucleases C2 and T1). This may be because of the non-polar environment of the tryptophan residues in these proteins or because of the absence of dipole-orientational broadening of spectra. The effect was also not found for proteins emitting at long wavelengths (max. at 341-350 nm)-melittin at low ionic strength, IT-Aj1 protease inhibitor, myelin basic protein. In these proteins, the tryptophan residues are exposed to the rapidly relaxing aqueous solvent. Spectral shifts associated with red-edge excitation are observed for proteins emitting in the medium spectral range - human serum albumin in the N and F forms, IT-Aj1 protease inhibitor at pH 2.9, melittin at high ionic strength as well as the albumin-dodecyl-sulfate complex. This suggests the existence in these proteins of a distribution of microstates for tryptophan environment with various orientation of dipoles and of slow (on the nanosecond time scale) mobility of the field of these dipoles. As a result the emission proceeds from electronic excited states which are not at equilibrium.

Proteins↗
PubMed1985

Nanosecond dynamics of charged fluorescent probes at the polar interface of a membrane phospholipid bilayer.

Molecular relaxation fluorescence methods were applied to analyze the nature and characteristic times of motions of amphiphilic molecules absorbed in the polar region of a phospholipid bilayer. The fluorescence probes 2-toluidinonaphthalene-6-sulfonate and 1-anilinonaphthalene-8-sulfonate in egg phosphatidylcholine vesicles were studied. The methods of edge excitation fluorescence red shifts, nanosecond time-resolved spectroscopy, fluorescence quenching by hydrophilic and hydrophobic quenchers and emission wavelength dependence of polarization were used. The structural (dipolar) relaxation is shown to be a very rapid (subnanosecond) process. The observed nanosecond phenomena are related to translational movement of the chromophore itself towards a more polar environment and its rotation. The polar surface area of the phospholipid membrane appears to be a highly mobile liquid-like system.

Egg Yolk↗
PubMed1983

Age-dependent changes of protein structure. The properties of young and old rabbit aldolase are restored after reversible denaturation.

The significantly increased helical content is observed in muscle aldolase molecule of old rabbits. The unfolding and refolding of protein conformation followed by circular dichroism, fluorescence and enzyme activity showed the recovery of initial conformation after the denaturation. The protein folds into the form that existed prior to denaturation--"young" into "young" and "old" into "old"--the conformational differences between them being restored. This suggests that the primary structure modifications prior to the folding of the native protein conformation are the origin of the age-dependent differences of aldolase structure and function.

Aging↗
PubMed1982

On the nanosecond mobility in proteins. Edge excitation fluorescence red shift of protein-bound 2-(p-toluidinylnaphthalene)-6-sulfonate.

The fluorescence of 2-(p-toluidinylnaphthalene)-6-sulfonate associated with beta-lactoglobulin, beta-casein, and bovine and human serum albumins are shown to depend on excitation wavelength. A long-wave shift of the spectra is observed at the long-wave edge excitation, reaching 10 nm and above. A similar phenomenon is found in glucose glass and in glycerol at +1 degrees C, i.e., in systems with delayed dipolar solvent relaxation, but not in liquid solutions. This phenomenon is proposed to be based on relaxation processes in the excited state. There exists a distribution of chromophore microstates with different interactions with surrounding groups which results in heterogeneous broadening of the electronic spectra and allows photoselection of a part of this distribution, being characterized by a low transition energy. The fast structural relaxation results in an altered distribution and, if this is the case, the effect of edge excitation of fluorescence spectra is not observed. If the structural relaxation during the excited state lifetime is absent, this effect is maximal. This interpretation is in agreement with results on the influence of red edge excitation on the low-temperature fluorescence spectra of dyes and with the data on time-resolved nanosecond fluorescence spectroscopy. The results of this work strongly support the significant dye fluorescence spectral shifts on protein binding, being determined not only by polarity changes in their environment, but also by relaxation properties of protein groups in this environment. These results also indicate that on the nanosecond time scale, the structural relaxation around the excited chromophore in proteins may be incomplete.

Animals↗
PubMed1977

Temperature-dependent changes of myeloma immunoglobulin G (K) IVA, Bence-Jones protein (K-type) IVA and its fragments.

1. The temperature function of the myeloma IgG(K) IVA, Bence-Jones protein (K-type) IVA and its fragments (Fab(t), Fc'(t), VL and CL) was studied by thermal perturbation difference spectroscopy and circular dichroism. 2. The IgG and Bence-Jones protein studied were found to be capable of a fully reversible structural changes at temperatures between 25 and 35 degrees C. The changes occurring at the higher temperature are accompanied by the screening of the significant part of exposed tyrosine residues. The transition is not accompanied by an appreciable change in the main IgG secondary structure-beta-pleated sheet, according to the CD data. 3. It was found that the temperature-dependent changes of IgG occur in its Fab fragments, the changes of Bence-Jones protein occur in its variable part (VL domains). 4. The temperature changes in the interval 25-35 degrees C are explained by the flexibility of amino acid side chains composed hypervariable loops delineated the "sides" of cavity between variable domains.

Bence Jones Protein↗
PubMed1975

Temperature and pH dependent changes of immunoglobulin G structure.

1. The temperature and pH functions of the myeloma IgG(K) conformation were studied by optical rotatory dispersion, circular dichroism, thermal perturbation difference spectroscopy, solvent perturbation difference spectroscopy, electrochemical iodination and difference adiabatic scanning microcalorimetry. 2. The IgG studied was found to be capable of a fully reversible structural change between pH 6.5 and 6.0. A transition occurring at low pH is accompanied by an increase of exposure of the chromophores to the solvent. 3. The "alkaline state" was found to be capable of a fully reversible S-like transition at temperatures between 25 and 35 degrees C. The changes occurring at the higher temperature are accompanied by the screening of 14-15 tyrosine residues and probably by a small increase in the helicity of the protein. These changes are not accompanied by an appreciable heat effect. The thermal denaturation of the "alkaline state" occurs only at 64 degrees C in the narrow temperature interval (3-4 degrees C). 4. The "acid state" is not accompanied by S-like transition at 25-35 degrees C. The thermal denaturation of the "acid state" occurs at 54 degrees C in the wide temperature interval (8-9 degrees C). 5. It was proposed that the ionisation of the invariant histidine residues situated in the "cavity" between the constant and variable domains causes the pH transition studied. The temperature changes in the interval 25-35 degrees C are explained by the alteration of the domains interposition. Similar alterations were investigated as a result of antigen-antibody reaction.

Animals↗
PubMed1975

On the effect of temperature on the ultraviolet spectra of protein chromophores.

The thermal perturbation difference spectra - TPDS (15-30 degrees C) - of N-acetyl-tyrosine-ethyl ester and o-methyl-N-acetyl-tyrosine were studied in ethyl acetate and dimethyl ether with/without the addition of butanol which served as a proton donor in hydrogen bonding. In all cases the longwave shift of the absorption spectrum is shown to be a principal factor that determines the origin of TPDS and the hydrogen bonding has no effect on these spectra. These results contradict the view that the red shift of protein chromophore spectra at the elevation of temperature is a unique feature of water as a solvent. The water-inaccessible chromophores in proteins may be perturbed by temperature increase, producing red shift.

Journal Article↗
PubMedDate not supplied

Recognition between flexible protein molecules: induced and assisted folding.

This review focuses on a very important but little understood type of molecular recognition--the recognition between highly flexible molecular structures. The formation of a specific complex in this case is a dynamic process that can occur through sequential steps of mutual conformational adaptation. This allows modulation of specificity and affinity of interaction in extremely broad ranges. The interacting partners can interact together to form a complex with entirely new properties and produce conformational signal transduction at substantial distance. We show that this type of recognition is frequent in formation of different protein-protein and protein-nucleic acid complexes. It is also characteristic for self-assembly of protein molecules from their unfolded fragments as well as for interaction of molecular chaperones with their substrates and it can be the origin of 'protein misfolding' diseases. Thermodynamic and kinetic features of this type of dynamic recognition and the principles underlying their modeling and analysis are discussed.

Animals↗