[Thermostability of DNA and its connection with the glassing process]. / Termostabil'nost' DNK i ee sviaz' s protsessom steklovaniia.

Using differential scanning calorimetry, the thermal denaturation of calf thymus DNA with different content of water (from 12 to 92%) was investigated. Dependences of melting temperature and enthalpy on the biopolymer hydration degree were established. Within the range of water concentrations from 92 to 50% the values of thermodynamic parameters of denaturation were obtained being in good agreement with the published data. Besides, a calorimetric manifestation of renaturation process at different cooling conditions after denaturation was studied. Special attention was paid to thermal properties of denatured and native DNA in the samples containing only the bound water. The temperature dependence of heat capacity in the denatured samples, which have completely lost their renaturation ability due to the proper thermal treatment, demonstrated a characteristic jump of thermal capacity. The value of this jump has been determined to be equal to 1.0 cal/g. degree C, related to dry weight, and almost not dependent on humidity. Temperature position of the jump (Tg) depends on the content of water which serves as a plasticizer. It is shown that the observed anomaly demonstrates all the properties characteristic of vitrification process in synthetic polymers and proteins. General similarity of thermal properties of the samples of native DNA, containing only the bound water, with those of denatured DNA also indicates a transition from the glassy into the rabber-like state. A possibility of existence of both native and denatured DNA in the glassy state at room temperature for the samples with low humidity (about 25%) has been demonstrated experimentally. It can be suggested that the formation of glassy state at dehydration of native DNA ensures its thermostability and the ability of restoration of its functional properties at a subsequent dehydration.

[Formation and melting of ordered structures in denatured myoglobin with differing water content: differential scanning calorimetry method]. / Issledovanie obrazovaniia i plavleniia uporiadochnnykh struktur v denaturirovannom mioglobina pri razlichnom soderzhanii vody: metod differentsial'noi skaniruiushchei kalorimetrii.

The possibility of superstructure formation in denatured globular proteins has been studied through the temperature dependence of the absolute values of heat capacity in the myoglobin-water system with water content from 80 to 25% in the temperature range 20-160 degrees C. For all the composition range studied it is found that after the denaturation of myoglobin the new regular structures with reversible melting are formed. These structures are similar in properties to the thermotropic gels in concentrated myoglobin solutions. Decrease of the water content influences the formation of these non-native ordered structures in denatured protein and increases the dispersion of its formation and melting temperatures.

[Thermal characteristics of a collagen-water system. II. Conformationalmobility of macromolecules in native and denatured states]. / Teplovye svoistva sistemy kollsgen-voda. II. Konformatsiai i konformatsionnaia podvizhnost' makromolekul v nativnom i denaturirovannom sostoianiiakh.

By calorimetric study of the collagen-water systems with 10-100% content of protein in the temperature range 20 + 90 degrees C we have measured the proper heat capacity of protein in native and denatured state. It is shown that S-like dependence of heat capacity on the water content for both native and denatured samples is caused by glass transition. At temperatures above the glass transition in moist collagen or above the denaturation of native collagen the translational mobility of segments in protein molecules appears. This mobility is most probably the cause of the increments in the temperature dependence of heat capacity. According to our results, for the denatured collagen the value of heat capacity in solution exceeds that for dry samples at least by the magnitude of heat capacity increment at glass transition.

[Thermal properties of collagen-water system. 1. Increments of heat capacity during denaturation and glass transition]. / Teplovye svoistva sistemy kollagen-voda. 1. Inkrementy teploemkosti pri denaturatsii i steklovanii.

The absolute values of heat capacity of the collagen-water systems with different relative content of the components in both native and denatured state were studied by the method of differential scanning calorimetry in a wide temperature range (-40 +/- 140 degrees C) which includes the region of the denaturation phase transition as well as the region of the relaxation glass transition. From the experimental data the values of denaturation increment delta Cpnd-0.42 +/- 0.04 J/(g.K) at the collagen content 10-50% and the values of glass transition increment delta Cpg-0.54 +/- 0.12 J/(g.K) for moist denatured protein were calculated. Different processes influencing the increment values are analysed. The nonequilbrium character of the glass-like state of moist proteins was clearly demonstrated in the study of glass transition.

[Melting of ordered structures in denatured collagen depending on biological age by differential scanning calorimetry]. / Issledovanie plavleniia uporiadochennykh struktur v denaturirovannom kollagene v zavisimosti ot biologicheskogo vozrasta metodom differentsial'noi skaniruiushchei kalorimetrii.

Using the differential scanning calorimetry we were able for the first time to establish the correlation between the biological age of the collagen tissue (rat tail tendon, age from 20 days to 24 months) and the melting parameters of gels, which are formed after the collagen denaturation. We have found that the half-width of the gel melting curves delta T1/2, as well as the ratio of the gel melting heat to the denaturation heat Qm/Qd are sensitive to the biological age of the tissue. The gel melting temperature Tm, in distinction to the denaturation temperature, was found to be not sensitive to the age but entirely dependent on the gel formation temperature. As it was experimentally demonstrated the above mentioned correlations can be observed only at well characterized thermal prehistory of samples and strictly fixed regime of gel formation.

[Parameters of heat disruption of native collagen structures and their connection with biological growth]. / Parametry teplovogo razrusheniia nativnykh struktur kollagena i ikh sviaz' s biologicheskim vozrastom.

By means of differential scanning calorimetry we have studied the influence of structural changes induced by the biological aging on the processes of thermal denaturation of collagen tissue (rat tail tendon, age from 14 days to 24 months). We have found that some parameters of the thermal denaturation process, namely, the denaturation temperature Td and the denaturation heat Qd are sensitive to the biological age of the tissue. Both Td and Qd are increasing with the age. However, this increase takes place only on early stages of aging. When the denaturation heat Qd of the tissue is normalized on the content of collagen in it, one obtains the independent on the age value of 75 J/g. So the increase of Qd with aging reflects the increase of the collagen content in tissue. We have found that the half-widths of the denaturation curves delta T 1/2, as well as the heat capacity increment at denaturation delta Cp do not depend on the tissue age. Both for fibrills of collagen and for its solution the measured value of delta Cp is equal 0.42 +/- 0.004 J/g degrees C which differs considerably from the earlier published data.

[New data on heat denaturation of collagen fibrils]. / Novye dannye o temlovoi denaturatsii fibrill kollagena.

Using the differential scanning calorimetry we have found that the structural changes due to the aging have the influence on the temperatures of denaturation and the values of denaturation heats of the intact collagen (rat tail tendon). The magnitude of the specific heat jump at denaturation of the collagen fibrills differs from that for the isolated molecules.

[Calorimetric study of the formation and melting of thermotropic gel in solutions of globular proteins]. / Kalorimetricheskoe issledovanie obrazovaniia i plavleniia termotropnogo gelia v rastvorakh globuliarnogo belka.

Scanning calorimetry has been used for studying lysozyme water solutions of different buffer molarity (mu = 0.5 divided by 1.0) and concentrations (c = 1.5 divided by 25%) at pH 2.0. It is shown that an additional high temperature maximum (HTM) can be observed on the heating curves for lysozyme solutions during irreversible denaturation. Calorimetric and rheological studies under identical heating conditions have shown that aggregation of protein during denaturation leads to the formation of the thermotropic gel. Further increase of temperature brings up the melting of this gel which results in the appearance of HTM on thermograms. Slow cooling of lysozyme gel melt leads to its reconstruction which results in the appearance of exothermic maximum on the corresponding thermograms.

[Temperature and time stability of proteins in concentrated solutions]. / Temperaturno-vremennaia ustoichivost' belkov v kontsentrirovannykh rastvorakh.

A comparative calorimetric study of temperature stability of proteins in reversible and nonreversible denaturation has been carried out by means of continuous heating of its concentrated solutions. A wide range of heating rates (vh) was used. The dependence of denaturation temperature Td on the total heating time is quite different in cases of reversible (RNase, Ph 4) and nonreversible (catalase, PH 7) denaturation. At moderate heating rates (vh less than 5 deg/min) the temperature Td does not depend on vh for reversible denaturation in contrast to nonreversible denaturation where Td decreases with the decrease of vh. At high heating rates (vh greater than 10 deg/min) Td increases along with heating rate for both types of denaturation. It is assumed that the dependence of Td on the heating time for catalase at low and moderate heating rates is caused by the nonreversible nature of denaturation process. The increase of Td with vh at high heating rates is connected with superheating of native structure for td greater than 1 degree/vh.

[Calorimetric study of the fusion of the liquid-crystalline structure of poly-gamma-benzyl-L-glutamate solutions]. / Kalorimetricheskoe izuchenie plavleniia zhidkorkristallicheskoi struktury rastvorov poli-gamma-benzil-L-glutamate.

A calorimetric study has been carried out of the specific features of melting of liquid-crystalline structure in the system PBG--dioxan depending on the conditions of its formation on the one hand, and on destruction rate on the other. It has been found that an increase of the temperature of solution crystallization as well as an increase in crystallization time shifts the conformation transition to the region of high temperatures, the value of the temperature shift decreasing with the rise of multiplication of heating for all the concentrations studied. By means of kinetic studies a sharp increase of heat effect with the rise of the velocity of heating the system has been found. A change in the scanning rate does not displace the beginning of the conformation transition, while Tmax and Tult is increased with an increase of Vheat. The kinetic regularities obtained allowed to suggest the presence of two processes proceeding when the system studied is passing the interval of conformation transition--the melting processes and subsequent aggregation of PBG molecules. They allowed also to separate these two processes.