From Big Medical Encyclopedia

TsITOHROMY (Greek kytos a receptacle, here — a cell + chroma color, coloring) — group of the gemsoder-zhashchy proteins having property to accept and give electrons due to change of valency of the central atom of iron in gem. In group C. the connections which are carrying out various biol enter. functions and taking part in such major cellular processes as tissue respiration (see biological oxidation) and oxidation by different molecular oxygen of unpolar organic compounds (see). Biol. the role of nek-ry tsitokhrom is not clear though, apparently, all of them function by consecutive oxidation and recovery (see Redoxreactions). Nek-rye Ts. is considered to be respiratory enzymes (see), and others — simply carriers in processes of oxidation and recovery.

Absorption spectrum of system C., typical for a number of animal fabrics, with four strips in a visible part of a range for the first time observed Mac-Mann (Page A. MacMunn) in 1886. However only in 1925 could estimate D. Cailyn biol. a role of these gem-containing proteins (hemoproteins). The term «tsitokhroma» accepted by biochemists of all countries was also offered them. Established D. Cailyn to the first that the tsitokhromny system plays an important role in processes of tissue respiration and biol. oxidations.

C. contain almost in all plant, animal and bacterial cells using the energy which is released in process biol for the life activity. oxidations. Carry all intracellular hemoproteins to tsitokhroma (see Metalloproteins), except for hemoglobin (see), a myoglobin (see), catalases (see) and peroxydase (see).

Classification of C. it is based on distinctions in the nature of their prosthetic group — gem. According to four types gem allocate four groups C., tsitokhroma and, with, d, to-rye differ with side chains at porphyrinic rings (see Porphyrines). At tsitokhrom and the gemovy group contains a formylation side chain, at tsitokhrom of Kommersant prosthetic group is the hematin not covalently connected with a proteinaceous part of a molecule, at tsitokhrom about side chains gem are covalently connected with protein, and at tsitokhrom of d of gems contains dihydroporphyrine (chlorine). If in a molecule of cytochrome two different gemovy groups are connected with specific protein, then specify both types of gem in the name of this cytochrome, napr, CD cytochrome (Pseudomonas cytochrome oxydase; KF

If in a molecule of a hemoprotein atom of iron is koordinatsionno connected not only with four nitrogen atoms of porphyrine, but also with certain groups of protein (the fifth and sixth coordinate bonds), then in designation C. there is no sign «stroke», napr, in cytochrome with one of coordinate bonds another forms from the rest of a histidine (see), and — from the rest of methionine (see) a proteinaceous part of a molecule. In designation of tsitokhrom, at to-rykh the nature of bonds of gemovy group differs from described above, the sign «stroke» is used (e.g., cytochrome with').

Name C. with the established structure includes the numerical index standing at the letter designating subgroup to a cut this cytochrome, napr, cytochrome a3 belongs (cytochrome with — an oxidase: KF At designation of other C. specify wavelength (in nanometers) a-strips in an absorption spectrum got into condition (e.g., cytochrome with-554). Wavelength is determined at the room temperature and give its value for absolute (but not differential) an absorption spectrum.

C. in got into condition possess accurately expressed characteristic absorption in the visible range of a range. In a typical absorption spectrum individual cyto -

Fig. 1. The graphic representation of absorption spectrums oxidized (solid line) and recovered (dashed line) of forms of cytochrome with: on abscissa axis — wavelength in nanometer, on ordinate axis — the size of an extinction in cm2/molj\and, r and

7 — maxima of absorption. On graphics of absorption got into condition cytochrome with clearly the peaks corresponding to three characteristic strips of absorption are visible: and - a strip of 550 nanometers, a r-strip

of 520 nanometers and a v-strip of 415 nanometers. As a result of oxidation got into condition cytochrome about absorption in the area and - and r - on - los becomes diffusion, maxima disappear, the v-strip remains, but becomes less intensive and is a little displaced towards an ultra-violet part of a range.

chrome (in the recovered state) there are three main strips of absorption. As reduction of wavelength they are designated as and - r-and at - strips. The most intensive is at - a strip; and - the strip which usually have on graphics an appearance of acute peak, more intensively, than (Z - hollow sa. It should be noted that the r-strip of absorption at tsitokhrom and is expressed very poorly, and sometimes and absolutely is absent. As a result of oxidation got into condition by C. and - and P-strips disappear and absorption in this area becomes diffusion; the ^-strip remains, but is a little displaced towards an ultra-violet spectral range (fig. 1).

Localization of C. in cells varies depending on specialization of cells and from intensity of their functioning. Most part of cellular C. it is localized in an inner mitochondrial membrane (see Mitochondrions) and in microsomes (see) — membranes of a cytoplasmic reticulum, in plasma membranes, in membranes of chlorolayers, and also partially in a nuclear membrane. E.g., in flying muscles of insects of C. are located almost only in mitochondrions (in an inner mitochondrial membrane) while in cells of a liver a considerable share of all C. is in membranes of a cytoplasmic reticulum.

The electron transport chain in mitochondrions schematically looks as follows:

substrate (NAD-N, succinate, etc.) -> “>On(FeHr) - >>K0Q-4HT0xp0M b->Cj-^цитохром cytochrome with -> cytochrome aa3 -» oxygen 02,

where FP (FeHr — flavo-proteidny enzyme, specific to a certain substrate, about the Crimea is connected negemovy iron, KoQ — ubi-quinone, or a coenzyme of Q.

In turn participation of C. in system of oxidation in microsomes it can be presented to one of possible schemes:

where RH — the oxidized substrate, FPH — a yellow enzyme 1, or NA DF • A N-dehydrogenase.

Enzymes, being electron donors for tsitokhrom, carry the group name a tsitokhromreduk-basin. For example, OVER • N-tsitokhrom b — reductase, 5 cytochrome — reductase (KF, being oxidized, recover the corresponding tsitokhroma.

By the main methods of studying of functional activity of C. and their quantitative contents in -

them the spectral methods based or on measurement of intensity of the strips of absorption which are got into condition by C are., or on definition of a difference spectrum of absorption between the recovered and oxidized forms (see. Spectral analysis). Intensity of a-strips in an absorption spectrum characterizes degree of a vosstanovlennost of different C. even then, when they are in native fabrics and suspensions of cells.

The main complexity during the studying of C. is in what most of them it is difficult to receive in solution. Except for cytochrome with, the most part to-rogo is easily extracted, C. it is possible to allocate only by means of such rigid methods as processing of cells with ultrasound, detergents (see), and also by enzymic hydrolysis. The cleared C. do not react with each other during the mixing if at the same time at the same time do not add phospholipids to reaction mixture (see Phosphatides).

The most characteristic representatives of C. tsitokhroma with are and 65, R-450 cytochrome and cytochrome oxydase.

Cytochrome with is the most studied C. It is capable to be dissolved well in water. This cytochrome has a pier, small for protein. weight (apprx. 13 Ltd companies), is allocated in a crystal view from many biol. sources, and in each case its primary structure (i.e. the sequence of connection of the amino-acid remains in a proteinaceous molecule) is completely established. Comparison of primary structures of tsitokhrom from different biol. types showed surprising constancy of the sequence of the amino-acid remains in their polypeptide - ache chains; only the small number of provisions is noted, in to-rykh there can be a replacement of separate amino acids. Therefore cytochrome with is a convenient object for studying of points of divergence on an extent biol. evolutions.

Cytochrome with, like other C. with small a pier. it is powerful, in essence is a carrier in oxidation-reduction processes, transporting oxidation-reduction equivalents from one molecule to another as it does OVER (see N ikotinamidade-nindinukleotid). Therefore cytochrome with can be considered a true cofactor of a respiratory chain. He does not act as the enzyme activating specific substrate (see Enzymes).

Tsitokhromok of the SI of a basin (synonym: cytochrome aa3, cytochrome with — an oxidase; KF catalyzes oxidation of cytochrome with molecular

oxygen and is a final tsitokhromny component in a respiratory chain of mitochondrions (see). It is localized in an inner membrane of these organellas and strongly connected with the membrane. Cytochrome oxydase of an inner membrane of mitochondrions of a cardiac muscle of a bull contains six different proteinaceous subunits designated by numbers from I to VI. Homogeneous drugs of proteinaceous subunits of this cytochrome oxydase were emitted with method of an electrophoresis (see) in polyacrylamide gel with dodetsilsulfaty sodium. They have hydrophobic properties, are defined their pier. weight and amino-acid structure.

One of gemovy groups of cytochrome oxydase (gems a3) can connect respiratory inhibitors — monoxide of carbon (carbon monoxide gas) or cyanhydric acid (see), changing at the same time the absorption spectrum; and these inhibitors does not connect gems.

The c and t about x r about m of R-450 represents absolutely special class C. It is key enzyme

of Fig. 2. The graphic representation of absorption spectrums oxidized (/), recovered (II) forms of R-450 cytochrome and a complex got into condition R-450 cytochrome with monoxide of carbon — carbon monoxide gas (III): on abscissa axis — wavelength in nanometer, on ordinate axis — the size of an extinction. Difference of a range of the recovered and oxidized forms of R-450 cytochrome from a typical absorption spectrum of tsitokhrom is visible (see fig. 1). Clearly only the v-strip is expressed, at 450 nanometers there is a maximum of absorption not of the R-450 cytochrome, but a complex its got into condition with carbon monoxide gas.

metabolism of unpolar connections of an exogenous and endogenous origin at animals and the person. Its name «R-450 cytochrome» does not correspond to the nomenclature, however it remained in world biochemical literature. R-450 cytochrome represents a hemoprotein, to-ry

contains gems of Kommersant. The absorption spectrum its got into condition is not typical for tsitokhrom (fig. 2). R-450 cytochrome does not absorb light at the wavelength of 450 nanometers as it would be possible to assume according to its name; the strip of absorption in this area is inherent to a complex got into condition with monoxide of its SO carbon. Affinity of R-450 cytochrome to WITH much higher, than at cytochrome a3.

R-450 cytochrome carries out oxidation reactions by molecular oxygen of unpolar organic compounds. On the nature of action this cytochrome is the mono-oxygenase of external type using NADF*N as a source of oxidation-reduction equivalents. The oxidation reaction of organic compounds catalyzed by this cytochrome proceeds according to the equation:

RH-f 02+DH2 — ROH + n2 + D,

where RH — the oxidized substance, and DH2 — the donor of oxidation-reduction equivalents.

In zooblasts and the person R-450 cytochrome is localized in membranes of a cytoplasmic reticulum, in an outer mitochondrial membrane and a nuclear envelope. There are many various isoforms of R-450 cytochrome (see Isoenzymes), only from a liver of a rabbit, e.g., are allocated to 20 various subfractions of R-450 cytochrome. In cells of a liver, lungs, skin, etc. person and animals R-450 cytochrome carries out oxidation reactions of unpolar alien connections (xenobiotics), including medicinal substances, promoting thus their removal from a hydrophobic zone biol. membranes (see Membranes biological). In steroid producing fabrics it carries out oxidation reactions of cholesterol (see) in steroid hormones (see), in a liver — biosynthesis of bile acids (see) from cholesterol. R-450 cytochrome participates in oxidation reactions of unsaturated fatty acids (see) and biosynthesis of prostaglandins (see). The fermental systems including R-450 cytochrome, mnogokomponentna and, except it, contain NADF • N-spetsi-fichnye of reductase, negemovy sulfur-containing proteins or cytochrome of.

Cytochrome of — a typical hemoprotein of type £. Meets in all cellular membranes, except for an inner membrane of mitochondrions. It is capable to interact with molecular oxygen very slowly. The main biol. function of this C. it is not clear. He participates in monooksigenazny reactions, interacting with R-450 cytochrome, in reactions of desaturation saturated

fat to - t. Most likely,

OVER • N-tsitokhrom — the reduktazny system consists of this hemoprotein and OVER • A N-specific yellow enzyme (see Flavoprotpeida) is also the comprehensive reducing system of biological membranes

using oxidation-reduction equivalents of NAD-N for recovery oxidation of proteinaceous and nonprotein functional groups.

Histochemical methods of definition of tsitokhrom. Cytochrome oxydase and its substrate — cytochrome with are histochemical revealed by means of so-called G-nadi-reaction or la

of bilny nadi-reaction, oxidizing reaction between and - naphthol and a dimethyl-gs-phenylenediamine with education Indo-phenolic blue. This reaction is carried out on the fresh fixed fabric. Education Indo-phenolic blue in G-nadi-reaction is catalyzed by cytochrome with, oxidation to-rogo molecular oxygen goes slowly and for acceleration demands presence of cytochrome oxydase. Thus, positive G-nadi-oksidaznaya reaction demonstrates presence at the studied fabric of system cytochrome oxydase — cytochrome of page. The lack of cytochrome with can interfere with normal course of this reaction. The structures having enzymatic activity are painted in blue, bluish-violet, bluish-brown and brownish-black color depending on the used modification of reaction. From modifications of G-nadi-reaction modification Bør groan (a method of an oxidizing combination) is more often applied to definition of cytochrome oxydase — cytochrome with. As the used amine in this reaction apply a N-phenyl-gs-phenylenediamine, and as the agent of a combination, except and - naf-tolite, a number of various replaced naphthols.

Reactions by gistokhy. identifications of C. recommend to carry out in the neutral or alkalescent environment (pH 7,0 — 8,0). As inhibitors of activity of C., the control drugs used for production, usually use sodium azide or potassium cyanide.

See also Enzymes.

Bibliography: Archakov A. I. Micro

somalny oxidation, M., 1975; Dickson M. and Webb E. Enzymes, the lane, with English, t. 2, page 692, M., 1982; L about y d and 3., Gossrau R. and Shibler T. Gistokhimiya of enzymes, Laboratory methods, the lane with English, page 192, M., 1982;

Pearce E. A histochemistry, the lane with English, M., 1962; To e i 1 i n D. On cytochrome, respiratory pigment, common to animals, yeast, and higher plants, Proc. roy. Soc. B, v. 98, p. 312, 1925—1926;

M a c-M u n n C. A. Researches on myohaematin and the histohaematins, Philos. Trans. B, V, 177, p. 267, 1886.

A. I. Archakov, H. H. Ivkov;

A. G. Ufimtseva (gist.).