CHLOROPHYLL

From Big Medical Encyclopedia

CHLOROPHYLL (Greek chloros green + phyllon a leaf) — pigments of plants, and also nek-ry microorganisms, with the help to-rykh catches energy of a sunlight and process of photosynthesis is carried out. Participating in photosynthesis (see), a chlorophyll plays huge biol. role.

There are four types of a chlorophyll: and, with and d. The higher plants contain a chlorophyll and and, brown and diatomic seaweed — a chlorophyll and and with, lavers — a chlorophyll of d. Besides, nek-ry photosynthesizing bacteria contain analogs of a chlorophyll — backteriochlorophylls. The magnesian complex of a porphyrinic cycle is the cornerstone of molecules of a chlorophyll (see Porphyrines). The rest of polyatomic alcohol of phytol is attached to one of pyrrol rings thanks to what a chlorophyll had an opportunity to be built in a lipidic layer of a membrane of chlorolayers.

Allocation of a chlorophyll in pure form and their division into two components (a chlorophyll and and Kommersant) was for the first time carried out by the Russian botanist M. S. Tsvet by means of the method of a chromatography developed by it (see). To them it was proved that in leaves of plants a chlorophyll is accompanied by a number of yellow satellites — carotinoids (see). The constitutional formula of a chlorophyll is established by Fischer (N. to Fischer) in 1940 M. V. Nentsky and his pupils proved chemical relationship of hemoglobin (see) and chlorophyll of plants. In studying fiziol. roles a chlorophyll


fishing K. A. Timiryazev's researches were of great importance. Full synthesis of a chlorophyll made independently from each other Shtrell (M. Strell) and Vudvord (R. Century of Wood-worcl) in I960 of.

A chlorophyll is the main component of the pigmental device of the higher plants, mosses, seaweed, photosynthesizing bacteria. Contents them in plants depends on a species of a plant, security with mineral food and other conditions. The quantity of a chlorophyll in plants fluctuates from 1,7 to 5% in terms of dry weight. Concentration them on a surface of a leaf determines absorption intensity by a plant of light if the level of a chlorophyll does not exceed 2 mg/sq.dm. At the maintenance of a chlorophyll from 3 mg/sq.dm and above the absorbtion coefficient of light approaches 97 — 100% and does not depend on quantity of a pigment.

In cells of a green leaf a chlorophyll is in special organellas — plastids, to-rye is called also chlorophyllous grains, or chlorolayers. Each chloroplast of a plant Mnium medium has the volume of 4,1 X 10-11 cm3 and contains 1,3-109 molecules of a chlorophyll, is limited by a double lipoproteidny membrane and is filled with a proteinaceous stroma. The alternating plates of protein and the painted pigmental and lipidic layers form inclusions in a stroma (grana). Distances between molecules of a pigment in thin mono - or dimolecular layers are small; each of couple of molecules can be connected with enzymes like cytochrome (see Tsitokhroma), capable to give an electron to a chlorophyll, and another — with an acceptor of an electron like ferredoksin.

Process of photosynthesis begins pigmental system of a plant with absorption of a light quantum. Participation of intermediate systems in a transfer chain of an electron is shown on the scheme:



where X — a chlorophyll, TsIT — tsitokhroma, FD — ferredoksin, FL — flavin systems, hv — a light quantum. In the functioning photosynthetic unit

process of migration of energy between various forms of a chlorophyll is important. Actively functioning photosynthetic unit contains 200 — 400 molecules of a chlorophyll,


to-rye work as the uniform svetoulavlivayushchy system absorbing one light quantum. For one cycle of work on each 3000 molecules of a chlorophyll one molecule of oxygen is released. It is established that spectrally various forms of a chlorophyll form a ladder of energy levels, on a cut the absorbed energy «flows down» to reactive centers. Spectral researches allowed to dismember forms of a chlorophyll on three basic groups (short-wave, long-wave and intermediate) according to their role in absorption and transfer of energy.

The subcellular particles containing backteriochlorophyll are also found in photosynthetic bacteria. These are the flattened disks to dia. 100 nanometers carrying the name chromatophores.

Structures of pigmentobelkovy complexes in the organization of photosynthetic membranes of various organisms, including bacteria, seaweed and the higher plants, are similar. Polypeptides of a hlorofillobelkovy complex are synthesized in chlorolayers; they consist of the main polypeptide about a pier. it is powerful (weighing) 73 000 and three minor about a pier. it is powerful (weighing) 47 000, 30 000 and 15 000 units.

Synthesis and updating of a pigment in the growing green fabric proceed with high speed. With age fabrics process of biosynthesis of a chlorophyll is slowed down. At the first stages of biosynthesis of a chlorophyll by condensation of two molecules-aminolevu-linovoy to - you form porphobilinogen — derivative a pirrola, a cut as a result of a number of transformations gives the connection containing a porphyrinic kernel — protoporphyrin. The direct predecessor of a chlorophyll — the protochlorophyllide containing atom of magnesium is formed of protoporphyrin. Then after accession of polyatomic alcohol of phytol the chlorophyll is formed.

Stages from porphobilinogen to protoporphyrin and from protoporphyrin to a chlorophyll and are carried out on one of two schemes:


The first reaction prevails in leaves bleached-out (i.e. grown in the dark) plants, the second — in green. End-stages of biosynthesis of the pigmental device accelerate with the participation of uniform polyfermental a chlorophyll-sin-tetaznogo of a complex. In this regard dependence of biosynthesis


of a chlorophyll on the speed of proteinaceous synthesis and braking by its inhibitors of synthesis of protein is natural. Synthesis of pigments is slowed down also at decrease in temperature and completely stops at a temperature below — 2 ° whereas photosynthesis continues also at negative temperatures, up to — 24 °. Process is broken at insufficiency of iron and excess of manganese.

Formation of a chlorophyll happens consistently through a chlorophyll and by oxidation. Reaction of transformation goes on light; an intermediate stage is education enzyme - a proteinaceous complex.

There are instructions on dependence of speed of response on work of an electronic and transport chain and according to the speed of generation of NADFN and NADN as hydrogen donators. There are not clear stages of synthesis on the site of inclusion of magnesium, transformation of Mg-porphyrines, and also etherifications by phytol of the rest nro-pionovy to - you the IV pyrrol ring.

Ability of green plants to form in the course of photosynthesis complex organic matters of carbon dioxide and water is defined by presence of a chlorophyll at them. At the same time the maintenance of pigments of a chlorophyll and and a chlorophyll of Kommersant does not depend on geographical features of the area. Maintenance of a chlorophyll and more podverzheko to influence of physiological and ecological conditions, than maintenance of a chlorophyll of Kommersant.

Changes of a chlorophyll in ontogenesis of plants are described. Their contents increases in tillering period, in a phase of blossoming and infructescence. It is possible to determine readiness of plants for blossoming by the level of a chlorophyll. After completion of growth processes accumulation of a chlorophyll stops, and updating of molecules of a pigment happens in chloroplast, being not connected with formation of new chlorolayers.

The principle of the photosensitizing action of a chlorophyll at photosynthesis was proved by K. A. Timiryazev also includes excitement of a pigment light with transition of a pigment to a singlet or triplet state and the subsequent reversible photochemical changes. The chlorophyll at different stages can serve as the photochemical donor or electron sink.

As the tetrapyrrole

structures containing in a complex connected atom of iron possess an important role in tissue respiration of mammals (see Hemoglobin), the chlorophyll and its metalderivatives (i.e. connections, to-rykh instead of magnesium are entered into structure copper, iron, zinc, cadmium or silver) use in medicine as antigipoksiche-sky means. Metalderivatives of a chlorophyll received the name «feo-fitinata». Their anti-hypoxemic effect is connected with tetrapyrrole structure and presence of atom of metal. Water-soluble drugs of a chlorophyll have antibacterial and antiviral activity, especially Ag-feofiti-nat. Hemopoietic, all-tonic properties are inherent in chlorophyllin of sodium, to-ry use also as a biostimulator.

See also Assimilation, Pigmental exchange, Pigments, Porphyrines.

Bibliography: Godnev of T. N. Hloro

fill, his structure and education in a plant, Minsk, 1963, bibliogr.; To r and with-novsky A. A. Levels of light regulation of photosynthesis, in book: Theoretical bases of photosynthetic productivity, under the editorship of. A. A. Nichiporovi-cha, page 23, M., 1972; Metsler D. E. Biochemistry, Chemical changes in living cell, the lane with English, t. 1 — 2, M., 1980; Problems of biosynthesis of a chlorophyll, under the editorship of A. A. Shlyk, Minsk, 1971; Shlyk A. A. Metabolism of a chlorophyll in a green plant, Minsk, 1965, bibliogr.; E igenberg K. Yo., Since about a s-m u n W. R. a. Chan S. I. Chlorophyll an in bilayer membranes, Biochim. biophys. Acta, v. 679, p. 353, 1982; Metabolic pathways, ed. by D. M. Greenberg, v. 2, N. Y. — L., 1967; Olson J. M. Chlorophyll organization in green photosynthetic bacteria, Biochim. biophys. Acta, v. 594, p. 33, 1980.

II. A. Verbolovich, V. P. Verbolovich.

Яндекс.Метрика