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Biomedical subjects

E I Tiktopulo

Publications and source records attributed to E I Tiktopulo.

At least 37 records · Page 2Linked to original sources
PubMedDate not supplied

[Collagen denaturation enthalpy--nonlinear function of 4-hydroxyproline].

The results of calorimetric measurements of denaturation of collagens with different imino acid content are reported. In contrast to the existing point of view that denaturation enthalpy is a linear function of 4-oxyproline content, a nonlinear dependence was revealed. It is suggested that the reason for the observed nonlinearity is triplets of the (Gly-Pro-Hyp) type. An increase of their content can cause a decrease in the denaturation enthalpy in accord with the water-bridge structure and due to the minimum enthalpy effect of stabilization of the triplets as compared to triplets of other type.

Animals↗
PubMedDate not supplied

[Temperature changes in ribonuclease].

Deuteroexchange kinetics of ribonuclease is studied by the change of IR-spectra in the range of 1400--1900 cm-1 at different temperatures in solutions with two pD values, 2.6 and 5.1. It is shown that in the pre-denaturational temperature range the enthalpy of unfolding is 1.5 kcal/mol, i. e. two orders lower than the enthalpy of unfolding in the denaturational temperature range (100--120 kcal/mol). Thus in the pre-denaturational range of temperatures the disclosure of a compact protein structure can proceed at the expense of separate non-cooperative disruptures of bonds. However, the concentration of these disruptures is so low that they cannot give an explanation to the observed pre-denaturational macroscopic changes of protein.

Animals↗
PubMedDate not supplied

[Conformational states of the water-soluble fragment of cytochrome b5. I. pH-induced denaturation].

Cytochrome b5 is a membrane protein that comprises two fragments: one is water-soluble and heme-containing, and the other is hydrophobic and membrane-embedded. The function of electron transfer is performed by the former whose crystal structure is known; however, its conformational states when in the membrane field and interacting with other proteins are still to be studied. Previously, we proposed water-alcohol mixtures for modeling the effect of membrane surface on proteins, and used this approach to study the conformational behavior of positively charged cytochrome c as well as relatively neutral retinol-binding protein also functioning in the field of negatively charged membrane. The current study describes the conformational behavior of the negatively charged water-soluble fragment of cytochrome b5 as dependent on pH. Decreasing pH was shown to transform the fragment state from native to intermediate, similar to the molten globule reported earlier for other proteins in aqueous solutions: at pH 3.0, the fragment preserved a pronounced secondary structure and compactness but lost its rigid tertiary structure. A possible role of this intermediate state in cytochrome b5 functioning is discussed.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

[Conformational status of apomyoglobin in the presence of phospholipid vesicles at neutral pH].

The conformational state of sperm whale apomyoglobin (apoMb) was studied at neutral pH in the presence of negatively charged vesicles using near- and far-UV circular dichroism, tryptophan fluorescence, differential scanning microcalorimetry, and fast performance liquid chromatography. Under these conditions, the apoMb structure undergoes transition from its native to an intermediate state. In this state the protein loses its rigid native structure but retains its secondary structure. However, the environment of tryptophan residues remains rather hydrophobic. This intermediate state of apoMb shows properties similar to those of its molten globule state in solution. It is shown that apoMb can bind to negatively charged phospholipid vesicles even at neutral pH. A possible functional role of this intermediate state is discussed.

Apoproteins↗
PubMedDate not supplied

[Structural changes in Cry3A delta-endotoxin from Bacillus thuringiensis var. Tenebrionis in alcohol solutions at pH 2.0].

Conformational changes in Cry3A delta-endotoxin caused by three different alcohols (ethanol, butanol, and isopropanol) were studied using the methods of circular dichroism, scanning microcalorimetry, and electron miscroscopy. It was shown that, in addition to the standard decrease in the native structure stability, the alcohols can cause a conformational transition that results in a sharp increase in the beta-structure content and a change in the environment of aromatic residues. The conformational transition is accompanied by intermolecular association, which leads to the appearance of oligomers in the form of short filaments. When the alcohols were removed, the oligomers dissociated again into monomers, but it is likely that the native structure either is not restored or is restored only in a small portion of molecules. The oligomer structure is rather cooperative, and its thermostability is higher than that of the initial structure. The disruption of this structure upon heating, observed as a heat absorption peak, is reversible.

Alcohols↗
PubMedDate not supplied

[Model phospholipid membranes affect the holomyoglobin structure: conformational changes at pH 6.2].

The influence of model negatively charged membranes on the sperm whale holomyoglobin structure at pH 6.2 has been investigated by different techniques (far and near UV circular dichroism, tryptophan fluorescence, absorbance at Soret band, differential scanning microcalorimetry and fast performance liquid chromatography). It is shown that the holomyoglobin structure undergoes a conformational transition from the native to intermediate state analogous to its apo-form. This state is characterized by the absence of a rigid tertiary structure and the native heme environment. At the same time, the content of alpha-helical secondary structure remains almost native. To change the holomyoglobin structure similarly to that of its apo-form in the presence of membranes, a higher molar phospholipids/protein ratio is required. The properties of holomyoglobin in the presence of negatively charged membranes resemble those of the molten globule state of its apo-form protein in aqueous solution. A possible functional role of the discovered non-native myoglobin state is discussed.

Animals↗
PubMedDate not supplied

[Study of conformational transformations in serum albumin by the method of scanning microcalorimetry].

Thermal denaturation of serum albumin in the alkali pH region is investigated by the scanning microcalorimetry method. It is shown that at pH 8.5 a macromolecule undergoes a conformational transformation as a result of which its thermal characteristics are changed qualitatively. The form which corresponds to lower pH values is denatured according to the smaller than all or none greater than model with an intensive sorption of heat. The form corresponding to higher pH values is denatured noncooperatively without heat absorption but with an essential increase of heat capacity.

Calorimetry↗
PubMedDate not supplied

[Number of hydrogen bonds in the structure of collagen].

The kinetics of hydrogen exchange of collagens from different animals was studied by the radioisotopic method (tritium) and infrared spectroscopy (deuterium). It has been shown that collagens from different animals (rat, pike, cod, carp, frogs) differ in amino acid composition and thermostability but are similar in the amount of slowly exchanged hydrogens. All the studied collagens have (1.00 +/- 0.05) very slowly exchanged hydrogens per triplet and (0.6 +/- 0.1) slowly exchanged hydrogens per triplet. Identifying the quantity of slowly exchanged hydrogens with the quantity of hydrogen bonds in the macromolecule, it can be concluded that collagens differing in stability do not differ by the quantity and composition of intramolecular hydrogen bonds.

Animals↗
PubMedDate not supplied

[Microcalorimetric study of the domain organization of serum albumin].

Scanning microcalorimetry was used for studying the melting of the structure of human and bovine serum albumins and their fragments. It was shown that the melting of the native structure of serum albumin observed by the excessive heat absorption is a complex process which is described by three simple transitions overlapping in temperature. This means that the serum albumin molecule consists of three more or less independent cooperative structures, domains.

Amino Acid Sequence↗
PubMedDate not supplied

[Mobility of collagen structure and temperature adaptation of animals].

The method of hydrogen exchange is used to determine the mobility of acid-soluble collagen molecules from animals with different physiological temperature in terms of equilibrium constants of the formation of micro-unfolding or fluctuating defects of the structure. It has been shown that mobility of the collagen structure correlates with the physiological temperature of the animal from whose tissue collagen was isolated and is mainly determined by the amino acid content of the collagen. It has been shown also that at physiological temperatures characteristic for a particular species the level of collagen mobility is of the same order despite their different thermostability. The conclusion has been drawn that the level of mobility is the main criterion at the natural selection of the amino acid composition of collagens in different animals.

Adaptation, Physiological↗
PubMedDate not supplied

[Thermodynamic study of guanylspecific ribonuclease C2].

Guanylspecific RNAse C2 has been studied thermodynamically using a microcalorimetry technique. It is shown that at ph varying from 5,0 to 8,0 the RNAse C2 solution in a cacodylate buffer contains about 30% of monomeric and about 70% of dimeric forms of protein, each of them melting as a single cooperative system. Moreover, studies of the influence of phosphate ions have shown that they stabilize the system by 3-4 degrees and transform it into a monomeric form.

Aspergillus↗
PubMedDate not supplied

[Microcalorimetric studies of temperature transitions in fibrinogen and its proteolytic fragments].

Melting of fibrinogen and its proteolytic fragments has been studied by differential scanning microcalorimetry. It has been shown that the fibrinogen molecule contains at least nine cooperative regions. One of them pertains to the central structural block (domain E), two of them are formed by the structures removed at proteolytic fragmentation and the others make part of the terminal structural blocks (domains D). A scheme of localization of melting regions in the fibrinogen molecule is proposed on the basis of the results obtained.

Animals↗