[Microcalorimetric study of intact nucleoproteins]. / Mikrokalorimetricheskoe issledovanie intaktnykh nukleoproteidov.

It has been shown that melting of native chromatin complex in tissues and cells is a one stage process with transition parameters Tm = 82 +/- 1 degrees C, delta Tm = 6 degrees C and Qm = (24 +/- 3) cal/g DNA. A conclusion is made that the difference in melting temperatures of chromatin complex and DNA, which is 12 cal/g DNA, corresponds to the melting of secondary and tertiary structures of chromatin. It is shown the destruction of significant part of the secondary and tertiary structures of chromatin by the chromatin complex isolation from tissues and cells.

[Heat denaturation of crystalline and dissolved leghemoglobin]. / Teplovaia denaturatsiia leggemoglobina v kristalle i rastvore.

Heat transitions in crystals of leghemoglobin (LH) are studied by means of scanning microcalorimetry and microscopy. It has been found that LH crystals do not melt and their loss of crystal lattice is due to the denaturation of protein globules inside the crystal. Peculiarities of the crystal state (as compared to the solution) are shown in an increase in the cooperative character of heat transition and relaxation time of the system. Subsequent consideration of different variants of correlation of two stages of heat absorption by LH crystals made it possible to determine the type of physical process proceeding in the object by the shape of calorimetric curve. Both observed peaks of heat absorption were grouped with intramolecular processes of different thermodynamic properties. The first peak of heat absorption is a manifestation of intramolecular mobility, both of individual protein segments in relation to each other and of individual segments of alpha-helical regions. Thus microcalorimetry allows a study of peculiar intramolecular dynamics of globular proteins precisely in the crystal state, because the crystal as if synchronizes the movement of individual molecules at the expense of the unification of their kinetic energy, surroundings and mutual orientation.

[Thermal denaturation of pepsin in crystal form and in solution]. / Teplovaia denaturatsiia pepsina v kristalle i rastvore.

Thermal transitions in pepsin crystals were studied by scanning microcalorimetry and microscopy. A sharp dependence of thermal transition parameters upon the heating rate was discovered. It was determined that during the heating of pepsin crystals it is possible to observe phase transition of the first order type. Thermal transition is connected only with the denaturation of protein molecules in the crystal. The absence of crystals melting was shown with the help of microscopy. The coincidence of equilibrium denaturation temperatures of pepsin in crystal and in solution was shown in direct calorimetric experiments. The results obtained point to the fact that intermolecular interactions do not give any contribution to the thermostability of hydrated supermolecular protein systems.

[Thermal properties of DNA and polydeoxyribonucleotides in a wide range of ionic concentration of neutral salts and a polymer]. / Teplovye svoistva DNK i polidezoksiribonukleotidov v shirokoi oblasti kontsentratsii ionov neitral'nykh solei i polimera.

deltaHm, deltaT, Tm of melting of polydesoxyribonucletides polydAdT,, polyd(A--T)d(A--T), polyd(A--C)d(T--G) and DNA with different basic composition in a wide range of (10-2--4.0 M) ions (C2H5)4N+, Cs+ and Na+ were determined by the method microcalorimetry. It was established that the difference in melting heats of deltaHpolydAdT--deltaHpolyd(A--T)d(A--T) being approximately 0.6 kcal/mol b. p. represents that part of the energy which is caused by the heterogeneity of Stacking of interaction between (formula: see text) pairs. It is shown that the narrowing of deltaTm with increasing DNA concentration is connected with the decrease of the difference of polyGC and poly AT melting temperatures, what is with the parameter TGC--TAT which characterizes the melting of a free macromolecule.

[Physical state of crystalline proteins. IV. Melting of trypsin and pepsin crystals]. / Fizicheskoe sostoianie belkov v kirstallakh. IV. Protsess plavleniia kristallov tripsina i pepsina

The nature of heat transitions in trypsin and pepsin crystals during their heating at various rates is studied. Heating is shown to bring about only the denaturation of protein molecules in crystals.

[Physical state of crystalline proteins. III. Structure of thermal heating curves]. / Fizicheskoe sostoianie belkov v kristallakh. III. O strukture krivykh teplovogo nagreva.

By microcalorimetry the processes proceeding in crystals of aspartate-transaminase and catalase during their termal heating have been studied. Decrease of temperature range within which heat is absorbed during a reduction of heating rate shows that the process of the destruction of crystal order is determined by the denaturation of protein molecules. A thin structure of heat absorption curve is found at some heating rates. It is found that during heating no perfection of defect crystallite structures takes place. The protein state in crystal is either equilibrium or quasiequilibrium.

Microcalorimetry of thermal denaturation of pepsin and trypsin in the crystal state.

Heating of pepsin and trypsin crystals was studied by scanning microcalorimetry. A sharp decrease in temperature, halfwidth and heat of transition with a decrease in heating rate was discovered. It was shown that thermal transition is connected only with the denaturation of protein molecules in the crystal and not accompanied by the crystal disintegration into separate molecules.

[Study of DNA melting in the region of the inversion of relative stability of AT and GC pairs]. / Issledovanie plavleniia DNK v oblasti inversii otnositel'noi stabil'nosti AT- i GC-PAR

Systematic data on the dependence of the melting curve parameters of DNA from different organisms on the concentration of salt (C2H5)5NBr have been obtained. The melting curves were studied by spectrophotometric as well as by microcalorimetric methods. The DNA melting range width is shown to pass through the minimum value delta0T = 0.6 +/- 0.1 degrees at the point of inversion of relative stability of AT and GC pairs that corresponds to the concentration of (C2H5)4NBr equal to 2.9 +/- 0.1 M. This concentration, as well as the value of delta0T, are the same for different DNA's of common chemical structure. The T2 and T4 DNA containing hydroxymethylated and glucosylated cytosine residues show an anomalous behaviour. The enthalpy of melting falls very slowly as the salt concentration increases. The possible causes of the observed value of delta0T are discussed. A conclusion is drawn that the main factor which governs the DNA melting process in the region of inversion of the relative stability of AT and GC pairs is the heterogeneity of stacking interaction between different base pairs.