The RELAXATION PHENOMENA in biological systems (Latin relaxatio easing, reduction) — the phenomena characterizing features of process of return of biological system to balanced state after cancellation of the factors which brought her out of this state. To R. I. such various processes as gradation belong to thermodynamic more favorable hypodispersion in system of the dissolved substance (salt, sugar, etc.), transfer and redistribution of the energy received by separate components of system within all system in general or in the environment etc. of R. I. play a significant role in processes of life activity of organisms at the different levels of their organization. River I. are carried out not instantly after removal of system from balance, and about a nek-eye by the delay determined by properties of this system. For R.'s description I. the so-called time of a relaxation characterizing time during to-rogo an initial deviation from balance is entered decreases in e time (at exponential law of return of system to balance).
R.'s example I., observed during physical. and physical. - the chemical processes proceeding in biological and model systems transition to a new stationary state of system enzyme — substrate after the shift of balance of biochemical reaction due to jump of concentration, temperature, pressure, influence of light etc. can serve. Registration of the changes in kinetics of a current of a biochemical rektion happening at the same time is used for identification of stages of enzymatic reactions and definition of the constants of speeds corresponding to them, for data acquisition about time of the conformational transformations happening in biological macromolecules during reaction etc. (see. Kinetics of biological processes ). River I. are inherent also to the water molecules and macromolecules of biopolymers having electrical dipole moment at action on them of constants or variation electric fields (see. Dielectric permeability , Polarization ). Studying of features of the dielectric relaxation proceeding at the same time is applied to the analysis of a condition of water in biological systems (on distinctions of time of reorientation for free and bound water) and for measurement of time of diffusion rotary motion of macromolecules in solutions. This size is connected about a pier. it is powerful (mass) of macromolecules and viscosity of the environment. Similar data, and also data on the internal movement in macromolecules of biopolymers (see. High-molecular compounds ) and in biological membranes (see. Membranes biological ) during the studying of mechanisms of their functioning receive also by means of a method of fluorescent probes (see. Luminescence ). For the same purposes use a method nuclear magnetic resonance (see), with the help to-rogo define time of a relaxation of kernels of the chemical elements which are a part of macromolecules or biologically important connections 1 1 H, 1 2 N, 6 13 With, 7 15 N, etc.), and for the connections having electronic paramagnetism or containing spin tags, methods electronic paramagnetic resonance (see).
Time of a relaxation characterizes mobility of various kernels or spin tags as a part of biologically important connections, biopolymers and separate components of biological membranes that is used also for establishment of their localization, napr, in solution or in various sites of a membrane. Besides, definition of time of a relaxation for protons of the intracellular water which is contained in samples of various fabrics can be used for diagnosis of malignant new growths and studying of mechanisms of carcinogenesis. These sizes, as a rule, it is much more in bioptata of tumors of patients with various forms of cancer, than in healthy fabrics that, apparently, is connected with growth of mobility of some components of cellular water, and also growth of mobility of the intracellular structures connecting water owing to their partial destruction or because of possible disturbance of interaction between macromolecules of biopolymers or more complex biological structures. On the basis of distinctions between values of time of a relaxation in tumors and healthy fabrics develop methods of a nuclear magnetic and resonant nondestructive testing for the purpose of detection for protons of water and a research of malignancies directly in an organism.
The term «relaxation» is used in physiology and medicine also for the characteristic of extent of relaxation or falloff of a tone of skeletal muscles (up to full immobilization or paralysis). At the same time the relaxation can be a consequence any pathologies. The artificial relaxation can be reached by use of the chemical substances influencing c. N of page (drugs, analeptics), and also special drugs — muscle relaxants (see).
Bibliography: Berezin I. V. and To l of the EU about in A. A. Practical course of chemical and enzymatic kinetics, M., 1976; Vladimirov Yu. A. and to Dobra of c about in G. E. Fluorescent probes in a research of biological membranes, M., 1980, bibliogr.; In about l to e M. V N matte. Molecular biophysics, page 25, etc., M., 1975; Liechtenstein G. I. Metod of spin tags in molecular biology, M., 1974; With e-dunov B. I. and Frank-Kamenetsky D. A. Dielectric permeability of biological objects, Usp. fizich. sciences, t. 79, century 4, page 617, 1963, bibliogr.; Mathur-De V of yo R. The NMR studies of water in biological systems, Progr. Biophys. Molec. Biol., v. 35, p. 103, 1979, bibliogr.
S. I. Aksenov.