[A microcalorimetric study of collagen hydrated water in a temperature range 20-100 degrees C].

A new method for determining bound water was developed, which is based on precise measurements of the enthalpy of water evaporation from a sample using differential scanning calorimetry.

[Collagen denaturation enthalpy--nonlinear function of 4-hydroxyproline]. / Ental'piia denaturatsii kollagena--nelineinaia zatukhaiushchaia funktsiia 4-oksiprolina.

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.

[Enthalpic denaturation of collagen satisfies the general relation of the change in Delta H(d) from Delta C(p) for proteins at zero hydroxyproline level]. / Ental'piia denaturatsii kollagena udovletvoriaet obshchei zakonomernosti izmeneniia Delta H(d) ot Delta C(p) dlia belkov pri nulevom soderzhanii oksiprolina.

One of the noticeable peculiarities of thermodynamics of collagen is an anomalous high magnitude of the enthalpy of denaturation delta Hd at a very low thermostability. Taking into account recent ideas about the role of hydrophobic interactions in determination of the thermodynamic function of protein denaturation, it is shown that the high magnitude of delta Hd of collagen in comparison with those of globular proteins can be explained by two factors: a significant contribution of residues of 4-hydroxyproline and small magnitude of hydrophobic interactions.

[Temperature dependence of the kinetics of renaturation of partially denatured collagen]. / Temperaturnaia zavisimost' kinetiki renaturatsii chastichno denaturi rovannogo kollagena.

By the method of optical activity it has been studied the temperature dependence of the triple helical refolding process of partially denatured collagen from the skin and swim bladder of the mirror carp, and also that of the rat skin. It is shown that reducing the renaturation temperature the triple helical refolding rate increases and is in perfect agreement with the earlier observed fact [1,2]. The temperature coefficient of the reaction rate in the investigated region of temperatures remains constant, this fact ought to point to the zero value of activity energy of cis-trans isomerization process since renaturation goes on without nucleation stage. The obtained data do not agree with the earlier measured value of the activity energy of cis-trans isomerization process at collagen full denaturation [3-5].

[Thermodynamic basis for the water-bridge structure of collagen]. / Termodinamicheskoe obosnovanie vodno-mostikovoi struktury kollagena.

A solution of the problem of topology of hydrogen bond net in a triple-helix of collagen is suggested on the basis of thermodynamic data on denaturation of phylogenetically different collagen, as well as on that of the earlier evaluation of the energy of OH-group 4-hydroxyproline bond. It is shown that only water-bridged collagen structure in the variant of Ramachandran school can explain both the change of thermal stability upon the extent of proline hydroxylation and the phylogenetic change of thermostability.

[The role of 4-oxyproline in the phylogenetic change of collagen thermostability]. / K voprosu roli 4-oksiprolina v filogeneticheskom izmenenii termostabil'nosti kollagena.

Analysing the data on imino acid content and thermostability of collagens distinguished phylogenetically it is shown that one hydroxyproline residue (per 100 residues) which is localized in the third position of the triplet increases thermostability per 0.6 degree in the average. The magnitude obtained exceeds the value 4 times (0.16 degree). This happens at the expense of hydroxylated proline in the third position.

[Thermodynamic parameters of fibril formation activation of evolutionary differentiated collagens]. / Termodinamicheskie parametry aktivatsii fibrillobrazovaniia évoliutsionno razlichaiushchikhsiia kollagenov.

Activation parameters of fibril formation of evolutionary differing collagens were investigated. It has been shown that in a heated solution formation of collagen fibrils of different origin proceeds in different temperature regions related with the environmental temperature of species range. Enthalpy and free energy of the activation of fibril formation were measured. The data obtained show that fibril formation is preceded by the conformation of the molecules. Biological significance of the correspondence between the temperature of denaturation and that of the species range is discussed. The above correspondence is the limiting expression of functional dependence of conformational flexibility on temperature. Directed selection realized in the course of evolution is required for maintaining the velocity of collagen synthesis at the constant level.

[The presence of a thermally stable domain in the spiral part of a collagen molecule]. / Nalichie termostabil'nogo domena v spiral'noi chasti molekuly kollagena.

It is shown that in 0,5 M NaCl 8 M CH3COOH heat absorption and the second structure alteration in a heated solution proceed between two stages following one another, and besides, salts not only decrease the macromolecule denaturation temperature in total, but produce different destabilization effect on different regions. The presence of the thermostable domain in the macromolecule helical part permits investigation of the folding mechanism of the triple collagen helix under partial denaturation. The localization and biological role of the stable domain in the triple helix formation are suggested.

[Denaturation of collagen in the presence and absence of nonspiral terminal segments]. / Denaturatsiia kollagena pri nalichii i otsutstvii kontsevykh nespiral'nykh uchastkov.

Difference in the mechanism of denaturation of collagen in the presence and absence of the terminal non-helical regions is shown.

[Thermodynamic and structural characteristics of partially denatured collagen]. / Termodinamicheskaia i strukturnaia kharakteristika chastichno denaturirovannogo kollagena.

Thermodynamic and structural parameters of partially denaturated collagen which had undergone denaturation of different degrees are measured. On the basis of comparative analysis of these data it is established that denaturation enthalpy and secondary structure degree are linearly linked. These investigations made it possible to determine special features of heat absorption curves as well. It is concluded that heat absorption at collagen denaturation must be followed by corresponding conformational alteration.

[Calorimetric study of the mechanism of uncoiling the collagen molecule in the presence of ions]. / Kalorimetricheskoe issledovanie mekhanizma razvertyvaniia molekuly kollagena v prisutstvii ionov.

Calorimetric and polarimetric studies of partially denaturated collagen in the presence and absence of one and two valence ions were performed. It is shown that in the presence of salt in partial denaturation of renaturated collagen the denaturation enthalpy is changed upon two steps. Both stages are followed by the conformational alteration. The denaturation enthalpy of the renaturated collagen is less than that of the native one, but in the presence of salts it is rather higher than in its absence. The study made possible to indicate that two-stage alteration of denaturation enthalpy is occurrence of denaturation products with partially reconstructed structure in which the salts take an active part.