DENATURATION

From Big Medical Encyclopedia

DENATURATION — essential changes of natural properties of substance under the influence of chemical or physical impacts. The term «denaturation» is applied usually to to proteins (see). Disturbance of native unique structure under the influence of temperature increase, the high hydrostatic pressure, ultrasound, ionizing radiation, sharp shifts of pH, addition of some chemical substances terminating noncovalent bonds (e.g., urea, salts of guanidine, trifluoroacetic or trichloroacetic to - t), is called the general term «denaturation of proteins». The internal orderliness maintained by system of noncovalent bonds between numerous structural elements is inherent to a molecule of complete protein. At D. such orderliness is broken. Covalent (chemical) bonds in a molecule of protein at D. are not affected, and primary structure of protein remains. Structures of high orders — secondary or tertiary — are broken completely or substantially. Change of a native condition of molecules, similar D. of proteins, is known as well for nucleic acids (see).

Biologically active proteins — enzymes, antibodies, etc. — at D. are inactivated. The fact that in the course of D. active centers — precisely organized sites of proteinaceous molecules directly responsible for corresponding biol, function are broken is the reason of it. Physical. - the chemical changes accompanying D. are also connected with disturbance of an ordered structure of protein. So, at D. spiralizovanny sites of a polypeptide chain are broken (in various degree) that is fixed by the corresponding spektropolyarimetrichesky shifts. Transition of a polypeptide chain of protein from densely packed into a chaotic and mobile state causes change of viscosity and other hydrodynamic properties of their solutions. The being able D., when the polypeptide chain becomes more mobile, the general reactivity of chemical groups increases. Not titrated (i.e. not reacting) sulphhydryl (SH-) and some other groups, present at many complete proteins, are usually titrated after. Interaction of proteins with nek-ry dyes sharply amplifies as a result of. Because of increase in availability and increase in reactivity of various chemical groups at D. extent of interaction between separate proteinaceous molecules very strongly increases. In the denatured condition of a squirrel easily aggregate, i.e. the denatured proteins easily are besieged, curtailed or latinisen. In the dissolved state after D. it is necessary to apply the solubilizing substances to preservation of protein — detergents (see), urea, etc.

D. of proteins usually is followed by significant increase in heat content and entropy (see. Thermodynamics ), though these changes depend on conditions of the environment. The system at D., apparently, contains only two forms of protein in the elementary cases — native and completely denatured. In process of D. protein passes from one form into another without noticeable formation of any intermediate forms and, therefore, all denaturatsionny transition of a proteinaceous molecule proceeds as uniform jump. In other cases the kinetics of a denaturation indicates education during reaction of several rather stable not native forms of protein that it corresponds to more difficult scheme of transition. But if at D. the molecule of protein undergoes several conformational transformations, then each of them is cooperative, i.e. includes a large number of the interdependent reactions consisting in education and a rupture of noncovalent bonds.

In last D. considered as irreversible process, as transition of protein to the state having the minimum level of free energy. Now it is well known that D. is reversible. Actually coming irreversibility is created as it appeared, the accompanying reactions — aggregation of protein, oxidation of SH-group with education new disulfide (S — S) bonds and so forth. If these reactions are adequately excluded, then the tendency to return of protein to a native state (renaturation) proves at once after cancellation of the denaturant agent.

If D. in essence represents physical. transition orderliness — a disorder, in a renaturation is brightly shown biol, feature of proteins — ability to self-organization, a way the cut is determined by a structure of a polypeptide chain, i.e. hereditary information. In the conditions of living cell this information probably is decisive for transformation of a chaotic polypeptide chain to time or after its biosynthesis on a ribosome in a native molecule of protein.


Bibliography: Belitser V. A. Macrostructure and denaturatsionny transformations of proteins, Uke. biochemical, zhurn., t. 24, century 2, page 290, 1962, bibliogr.; About l and M. Physical chemistry of a denaturation of proteins, the lane with English, M., 1968, bibliogr.; Birds y O. B N. Physical principles of self-organization of proteinaceous chains, Usp. sovr, biol., t. 69, century 1, page 26, 1970, bibliogr.; Anfinsen C. B. The formation and stabilization of protein structure, Biochem. J., v. 128, p. 737, 1972, bibliogr.; Anfinsen G. B. a. Scheraga H. A. Experimental and theoretical aspects of protein folding, Advanc. Protein Chem., v. 29, p. 205, 1975, bibliogr.; Morawetz H. Rate of conformational transitions in biological macromolecules and their analogs, ibid., v. 26, p. 243, 1972, bibliogr.

V. A. Belitser.

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