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Biomedical subjects

E A Burshteĭn

Publications and source records attributed to E A Burshteĭn.

At least 19 recordsLinked to original sources
PubMedDate not supplied

[Analysis of log-normal components of fluorescence spectra of prodan and acrylodan bound to proteins].

Steady-state fluorescence spectra of prodan and acrylodan covalently bound to cystein residue of Lys-Cys-Phe tripeptide in solvents of different polarity were analyzed. It was shown that the shape of spectral bands is well described by a log-normal function. Linear relations between three shape-determining parameters of the log-normal function (namely, the positions of spectral maximum and two half-maximum amplitudes) were revealed and evaluated for both fluorophores. This finding enabled us to present the shape of spectral bands of these fluorophores in any environment as analytical log-normal functions depending on only two parameters, the maximum position and the peak amplitude. The empirical uniparametric log-normal curve was used for the analysis of composite fluorescence spectra of prodan bound to bovine serum albumin and acrylodan covalently attached to actin or subfragment 1 of myosin.

2-Naphthylamine↗
PubMedDate not supplied

[Decomposition fluorescence spectra of tryptophan residues in proteins based on log-normal components by a least squares method].

An algorithm of decomposition of protein tryptophan spectra into components was developed. The spectral shape of components is described by a uniparametric log-normal function. Rise of certainty and accuracy of resolution of widely overlapping smooth spectral components (a typical uncorrect reverse problem) was achieved using several regularizing factors: (i) the set of experimental spectra used were measured at several quencher concentrations; (ii) the functional being minimized, along with the root mean square residuals of intensities, the term depending on the obedience to the Stern-Volmer law; (iii) an extra information is used--the number of experimental values greatly exceeds the number of parameters to be estimated. The minimum of functional is determined by a consecutive setting of all possible combinations of component spectral maxima values, which allows to avoid sticking in the local minima of noisy functional. The real experimental noise restricts the decomposition into not more than three components. The decomposition error does not exceed the experimental one. The algorithm functioning is illustrated by resolution of tryptophan fluorescence spectra of papain into one, two, and three components.

Algorithms↗
PubMedDate not supplied

[The component analysis of tryptophan fluorescence spectra of melittin during its oligomerization].

The oligomerization of melittin with increasing ionic strength and protein concentration was investigated using the methods of decomposition of its tryptophan fluorescence spectra into "elementary" log-normal components. At high ionic strength (up to 2 M KCl), the emission spectra of tetrameric melittin are well described as the sum of two log-normal components, suggesting the presence of tryptophan residues in two sorts of environment with greatly differing polarity. Measurements of fluorescence spectra by iodide showed that these two spectral components possess different Stern-Volmer constants, that is, the tryptophans emitting them have different solvent accessibility, which does not correlate with the crystallographic structure of tetrameric melittin. Moreover, in the oligomerization transition induced by ionic strength, the tetrameric intermediate is formed, which has log-normal spectral components with relative contributions differing from those in 2 M KCl.

Melitten↗
PubMedDate not supplied

[Functional role of parvalbumins in regulating Ca2+ in the contraction--relaxation cycle of vertebrate skeletal muscles].

On the basis of parvalbumin property to change Ca2+-binding constant within the pH-region from approxim-tely 7 to approximately 8 a hypothesis that parvalbumins are pH-regulated Ca2+-depot in muscles has been stated. The addition of parvalbumin to native actomysin complex at pH approximately 7 in the presence of ATP and Ca2+ results in partial inhibition of its superprecipitation. The change of pH up to approximately 8 leads to the restoration of actomyosin superprecipitation.

Actomyosin↗
PubMedDate not supplied

[Ricin structure: the study by the fluorescence quenching method].

To elucidate the details of pH-induced conformational transformation of ricin [I] in the region surrounding tryptophan residues, we studied parameters of fluorescence of the native toxin and its isolated A- and B-subunits at pH 4.0, 5.0 and 7.4. The studies were carried out using resolution of fluorescence spectra according to different degree of tryptophan accessibility to ionic (iodide) and non-ionic organic (acrylamide) quenchers. Application of the new method allowed to reveal three classes of tryptophan residues differing in their accessibility to quenchers alpha-residues are accessible neither to ions nor to organic molecules; beta-residues are accessible only to organic molecules; while surface gamma-residues are accessible to both types of quenchers. The fluorescence spectra were assessed for each class of tryptophan residues. The major part of them was shown to be localized in apolar rigid microenvironment. Fluorescence of ricin and especially of its isolated subunits proved to be strongly dependent on the pH value. At pH less than 5 the structure of B-chain loosens, this process being reflected by an increase in accessibility of tryptophan residues to quenchers. In acidic solution at least one out of seven tryptophan residues in the ricin molecule undergoes conformational transformation. Positive charge prevails in the regions surrounding quencher-accessible tryptophan residues. Binding of lactose leads to a slight compactization of the toxin structure that causes, in its turn, short-wave shifts of the fluorescence spectra and reduction of Stern-Volmer constants for intraglobular tryptophan residues.

Hydrogen-Ion Concentration↗
PubMedDate not supplied

[The effect of the medium on the functional and structural properties of serum albumins. III. Relation between the N-F1-, F1-F2- and F2-E transitions of human serum albumin and temperature and ionic strength].

Using fluorescence parameters of tryptophanyl and bound ANS, the acid-induced structural transitions of defatted monomeric human serum albumin were measured as pH-dependences from 6 to 2.5 in the wide range of temperature (10 to 45 degrees C) and ionic strength (from 0.001 to 0.2 M NaCl or 0.067 M Na2SO4). Temperature rise and decrease in ionic strength value result in the splitting of the N-F-transition onto two stages, N-F1 and F1-F2. The N-F1-transition is accompanied by the blue shift of tryptophanyl and ANS fluorescence spectra and increase in the ANS emission yield. The F1-F2-stage is manifested in an additional blue spectral shift and a sharp drop of the ANS emission yield, which is shown to be due to the lowering of albumin affinity for the dye. In the acidic-extension stage (F2-E), the spectra undergo a red shift which means that the nanosecond dipole relaxation of protein groups and bound water becomes faster. In the F2 from, the albumin affinity for ANS is significantly lowered; the association constant of the primary binding site is lower by an order of quantity and two secondary sites are practically disappeared. The complex effect of temperature, ionic strength and pH changes on the properties of ANS-binding sites is considered as a model of possible control influences of these factors upon the albumin transport of amphiphilic anions in organism.

Binding Sites↗
PubMedDate not supplied

[Effect of the medium on functional and structural properties of serum albumins. IV. The state of human serum albumin in the pH range from 5 to 10].

In order to investigate the effects of temperature and ionic strength on the N-B-transition and the alkaline denaturation of the human serum albumin, the pH-dependences of fluorescence position and relative yield of Trp-24 and of protein bound dye ANS were measured. The measurements were carried out at temperatures from 10 to 45 degrees C and ionic strengths (NaCl) from 0.001 to 0.2. The pH-induced structural transitions have different realization in environments of tryptophanyl and tightly bound ANS. The alkaline denaturation does not change the Trp-214 fluorescence. The N-B-transition gives rise to the slight polarity and/or mobility lowering in the Trp-214 environment (the shorter-wave-length spectral shift). Increase in the temperature and ionic strength induces the shift of the transition midpoint from ca. 8 to 8.7 and reduces the spectral shift amplitude. At low ionic strengths, the new structural transition in the Trp-214 environment is observed at pH change from 6.7 to 5.7. This transition is not observable using ANS fluorescence. The N-B-transition is accompanied by an enhancement and longer-wavelength shift of the ANS fluorescence spectra. The transition midpoint is independent of temperature, but is shifted to lower pH values at a decrease of ionic strength value. At ionic strengths less than or equal to 0.01 the shorter-wavelength spectral shift is seen at pH from 7.5 to 9, which seems to reflect the disulfide B-A-isomerisation. The alkaline denaturation gives rise to the sharp quenching of ANS fluorescence, probably due to the ANS binding site decomposition.(ABSTRACT TRUNCATED AT 250 WORDS)

Anilino Naphthalenesulfonates↗
PubMedDate not supplied

[Effect of the medium on the functional and structural properties of serum albumins. I. Effect of ionic strength on N-variant of human serum albumin].

The effect of ionic strength on the 1-anilino-8- naphtalene sulfonate (ANS) binding sites of the N-form of human serum albumin (HSA) was studied by means of the protein and ligand fluorescence. The parameters of the binding of ANS to HSA (the number of sites and the binding constants) were determined by two methods: by measuring the ANS fluorescence either (i) at increasing protein concentrations and constant ANS concentration, or (ii) at increasing ANS concentration and two constant protein concentrations (9.6 and 2.53 microM). An increase in the NaCl concentration results in a monotonous decrease of the ANS fluorescence yield of HSA-ANS complex, which could be interpreted in terms of two different effects: first, the direct collisional quenching interaction of Cl-ions with bound ANS located on the surface of HSA and, second, the ca. 10 per cent decrease of the number of bound ANS molecules due to the lowering of the ANS-HSA association constant values. The fluorimetric titration showed that at low ionic strength (0.008 M NaCl) HSA molecule has one strong ( lgKaI = 6.75-7.25) and two secondary sites with lower affinity ( lgKaII = 6.35). The increase in the NaCl concentration results in a decrease of the affinity for both kinds of binding sites (in 0.2 NaCl lgKaI = 6.3-6.7; lgKaII = 5.6-5.9). In contrast with NaCl, Na2SO4 induces only a limited decrease of the ANS fluorescence occurring within a narrow concentration range (from ca. 0.02 to 0.05 M Na2SO4, e. i. at ionic strengths from 0.07 to 0.15) and which can be described as a cooperative interaction of six SO4(2)-ions with a HSA molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

Anilino Naphthalenesulfonates↗
PubMedDate not supplied

[The effect of medium on functional and structural properties of serum albumins. II. The effect of temperature on the N-form of human serum albumin].

In order to investigate effects of temperature in the physiological range (from 10 to 50 degrees C) on structural, physical and functional properties of the N-form of human serum albumin (HSA), the temperature dependences of fluorescence parameters of Trp-214 residue of HSA and of the specifically bound dye ANS, as well as of association constants of ANS binding in the primary and secondary binding sites on HSA molecule were measured. The temperature-induced changes of these properties of HSA are essentially dependent on pH (7.0 or 5,6) and ionic strength (0.001-0.008 or 0.2 M NaCl). At pH 7.0 and 0.2 M NaCl the environment of Trp-214 remained invariant at temperature changes between 10 and 50 degrees C. On the other hand, the affinity to ANS of a primary binding site doubled and that of secondary ones halved. These affinity changes seem to be due, are least partly, to the heating-induced dissociation of Cl-ions, which are inhibitors of the primary dye binding. By lowering pH (to 5.6) and ionic strength the temperature-induced changes in the Trp-214 environment were observed. The changes are interpreted as indole group transition into the buried region, inaccesible to water (the "closing" of a structural slit). The affinity of secondary binding sites of ANS was halved.

Anilino Naphthalenesulfonates↗
PubMedDate not supplied

[Binding of Ca2+ ions to bovine alpha-lactalbumin. Intrinsic protein fluorescence changes].

Binding of Ca2+ ion to bovine alpha-lactalbumin molecule causes a conformational change reflected in an almost two-fold decrease of the fluorescence quantum yield and a rather pronounced spectral shift towards shorter wavelengths (by ca. 20 nm). The changes could be interpreted as a result of a transfer of highly exposed tryptophan residue(s) into a rigid internal part of the protein molecule containing effective quenching groups (probably, vicinal disulphide bridges). The Ca2+ binding constant evaluated from EGTA--and pH-titrations is (3-6) X 10(8) M-1. The results of the spectrofluorometric pH-titration of alpha-lactalbumin in the presence of various Ca2+ concentrations suggest that the well-known acid conformational change in alpha-lactalbumin is due in fact to a competitive replacement of the bound Ca2+ by three H+ ions (pK = 5.0 +/- 0.1) in the Ca2+ binding site.

Animals↗