From Big Medical Encyclopedia

PHOTOREACTIVATION (Greek phos, phdtos light + lat. re the prefix designating repetition, resuming - f activus efficient, active) — I UF-izlucheii-em recovery of viability of the biological systems damaged, as a result of the subsequent influence of light of more long-wave spectral range.

Phenomenon F. openly in 1949 the Soviet researcher I. F. Kovalyov and irrespective of it an amer. scientist Kelner (A. K Peg's ei). Ability to F. it is revealed at representatives of almost all groups of an animal and flora: cells prokariot, yeast, mushrooms, many vi-


Dov of plants, mollusks, reptiles, fishes, mammals, including the person.

Consider that F. arose at biol. objects as adaptive reaction for protection from UF-izluche-niya the Sun and genetically was fixed in process of evolution. It is revealed that at the people sick with a pigmental xeroderma (see the Xeroderma pigmental), the quantity of a photo of lyase — enzyme of photoreactivation is sharply reduced.

Action spectrum F. at different objects it is various: at one maximum F. causes light with a wavelength of 355 — 380 nanometers, in others — 430 — 480 nanometers.

At the heart of F. reaction of a monomerization of tsik-lobutanovy dimer of pyridine bases of DNA which are formed in molecule DNA under the influence of UF-iz spearing with participation of a photo of the lyase activated by light (300 — 600 nanometers) lies photoenzyme-tivnaya. Photolyase splits the dimeasures which are formed as at direct absorption by molecule DNA of radiation (240 — 310 nanometers), and as a result of a photosensitization (see) at influence of Uv-radiation (315 — 360 nanometers). Photolyase is emitted in pure form from colibacillus, yeast, and also cells of mammals, in particular from cells of marrow, leukocytes of blood and fibroblasts of skin of the person.

Reaction of a photo of lyase with DNA has two stages:

At the 1st (dark) stage, edges depends on temperature, there is a linkng of enzyme (E) with the sites of DNA containing pirimidinovy dimeasures (S), and formation of quite steady enzyme-subst-military complex (ES). At the 2nd (light) stage, with participation of energy of a light quantum of hv (this stage does not depend on temperature), reaction of a monomerization of pirimidinovy dimer proceeds actually, as a result cover a complex breaks up to free enzyme and the free pirimidinovy bases (a product P). At nek-ry biological objects F. it is connected with a monomerization of pirimidinovy dimer of molecules RNA.

In addition to enzymatic F., it is known so-called indirect F. at action of Uv-radiation in the range of 300 — 380 nanometers, carried out without participation of enzyme. Indirect F. it is found in nek-ry strains of colibacillus. It is caused by a growth inhibition of cells at long-wave UF-radiation and the increased efficiency of a tempo (ekstsizionny) reduction stage of structure of DNA connected with it.

High specificity enzymatic F. gives the chance to analyze participation of pirimidinovy dimer of DNA in mechanisms of lethal and mutagen action of Uv-radiation, and also other agents damaging DNA with its help (see the Reparation of genetic damages). On the basis of F. it is also shown that pirimidinovy dimeasures of DNA participate in an inactivation of nek-ry strains of colibacillus iod action of ionizing radiation of high energy (see. Ionizing radiation).

See also Fotobiologiya, Photochemical reactions.

Bibliography: V. D tinmen.

DNA repair and its biological value, page 13, etc., L., 1979; To about in and -

l ev I. F. Vliyaniye of the visible site of a range of a radiant energy on dynamics of pathological process in the cell damaged by ultraviolet rays, Uchen. zap. Ukrainians, ekspery. in-that glazn. Bol. of the academician V. P. Filatov, t. 1, page 385, Odessa, 1949; To about N e in S. V. and Bolotovsky I. D. Fotobiologiya, page 292, Minsk, 1979; Smith K. and Heneuolt F. Molecular photobiology, the lane with English, page 175, M., 1972; Sutherland J. Page of Photophysics and photochemistry of photoreactivation, Photochem. Photobiol., v. 25, p. 435, 1977; Sutherland J. C. a. o. Photoreac-tivating enzyme from Escherichia coli. Interactions with DNA and mechanism of action, Biophys. J., v. 32, p. 242, 1980.

G. B. Zavilgelsky.