YELLOW ENZYMES

From Big Medical Encyclopedia

FLAVOPROTEYDY (Latin flavus yellow + proteids; synonym: alloksa-zinovy proteids, yellow enzymes) — group of complex proteins, enzymes, to-rykh as prosthetic group are a part flavin nucleotides. T. are eurysynusic in an animal and flora and at microorganisms, they take part in metabolism of the main classes of organic compounds, play an important role in the course of biological oxidation (see biological oxidation). Proyetetichesky groups F. — flavin nucleotides of a fl of wine-nindinukleotid (FAD) or flavin mononucleotide (FMN) — play concerning F. a specific role of coenzymes (see); in their structure vkho-

dit hepatoflavin, or Riboflavinum (see). T. are pigments (see), in the oxidized form they are painted in intensively yellow color, in got into condition are colourless.

The first yellow enzyme was open it. biochemists O. Varburg and W. Christian who emitted the so-called yellow enzyme catalyzing oxidation of the recovered NADF from yeast — NADF-N. Later this enzyme received the name NADF • A N-dehydrogenase (KF 1.6.99.1). It was established that prosthetic group of yellow enzyme of Warburg is FMN. Afterwards all F. began to call yellow enzymes for their yellow color in the oxidized state. By the beginning of the 80th of 20 century

FAD and FMN strongly was known apprx. 80 various F. Obychno and are specifically connected with the corresponding proteins apoenzymes. The exception is made by an oxidase of D-amino acids (F the ABP proteid), for a cut partial dissociation on FAD and protein apoenzyme is characteristic. The way of accession of a flavin coenzyme to an apobelka can be various. In nek-ry cases of FAD it is connected to the rest of a histidine or cysteine in a molecule of protein a covalent bond. However more often the flavin nucleotide can be separated easily from protein processing by the concentrated salt solution at pH 2,0 — 4,0. Yellow enzymes consist of one or several polypeptide-nykh of chains (subunits) about a pier. it is powerful (weighing) from 12 000 to 800 000 and may contain one or several molecules of flavin nucleotides on each proteinaceous subunit. Fe2+ atoms, Mo2+, Zn2 +, etc. in addition support Nek-rye F. Special subclass F. make proteins, in to-rykh atoms of iron and sulfur atoms of the remains of cysteine interact, creating zhelezoserotsentra — Fe2S2-or the Fe4S4-centers.

T. represent the respiratory enzymes (see) belonging to the class oxide oreduktaz (see). The catalysis of oxidation-reduction reactions which is carried out F., it is caused by consecutive oxidation and recovery of their flavin components. Structure of an active center of an apoenzyme F., the enzyme creating the substratsvyazyvayushchy site on a molecule, activation of substrate and high substrate specificity of enzyme (see Enzymes), i.e. the nature catalyzed F is defined. reactions. Believe that as a part of F. partially got into condition flavin coenzymes are stabilized whereas in a stand-at-ease (in solution) they are unstable. The atoms of metals connected with an apoenzyme participating in the catalytic act provide reactions with such connections, to-rye do not interact with free flavin nucleotides or Riboflavinum.

Among simple F., consisting only of protein and flavin nucleotides, the oxidases of L-and D reacting with molecular oxygen - Amino-acids, glucose oxydas, monoamine oxidase (see), diaminoxidase are the most essential. Flavin dehydrogenases (see), as a rule, interact with oxygen only through intermediate carriers of electrons. These enzymes as, e.g., a suktsinatdegidro-genaza (see), can accept hydrogen not only from nicotinamide adenine dinucleotide (see), but also directly from substrates. As final electron sink of flavin dehydrogenases in cells serves the tsitokhromny system of mitochondrions (see Tsitokhroma). With the participation of flavin dehydrogenases electrons from NAD-N and amber to - you (succinate), formed in a cycle tricarboxylic to - t (see. Tricarboxylic acids a cycle), and also from KOA-pro-izvodnykh of fatty acids (see) and other substrates of oxidation (and - glycerophosphate, sincaline, methyl-aminoacetic acid) join in an elektronoperenosyashchy chain of mitochondrions (see) through the general acceptor — ubikhinon, to-ry at the same time it is recovered. Appeared this, testimonial that exist more difficult F., in to-rykh electron transfer in a respiratory chain it is carried out through the Re282-centers. The digidroorotat-oxidase (KF 1.3.3.1) belongs to such enzymes, e.g. As well as many other flavin oxidoreductases, this enzyme are formed by steady seven-quinone, participating in one-electron recovery of oxygen to superoxide-anion O (see Radicals free).

Are known to F., the catalyzing redoxreactions between the nikotinamidny nucleotides and proteins containing zhelezoserotsentra as the only prosthetic group (zhelezosulfoproteidama). It F. the enzyme found in mitochondrions of bark of adrenal glands of the person and animals and using NADF-N for recovery of a zhelezosulfoproteid of the adrenotoxin participating in a hydroxylation of steroids (see) is, e.g.

To number of the complex enzymes which are F., belongs a sulfitreduk-basin (KF 1.8.1.2), participating in assimilation of inorganic sulfite microorganisms, and the nitrate reductases (KF 1.6.6.1—3) which are carrying out recovery of nitrate to ammonia.

Are found by F., the containing tsitokhroma: the barmy lactate dehydrogenase (cytochrome) — KF 1.1.2.3 — consisting of 4 identical subunits is most known, each of to-rykh contains one FMN and one cytochrome of Kommersant. The oxidations of a lactate and recovery of cytochrome which are carried out by this enzyme with are among the processes delivering to cells energy (see the Lactate dehydrogenase).

Nek-rye F. (a lipoamiddegidroge-naza, a tioredoksinreduktaza) is transferred by electrons between nikotinamidny coenzymes and disulfides. These FAD-soderzhashchiye dehydrogenases consist of 2 identical subunits containing on one disulfide bridge (see Suljf-gidriljny groups).

Are found in anaerobic and photosynthesizing bacteria and blue-green seaweed simple F. — the flavodoksina containing FMN. These flavodoksina are recovered by hydrogenase or primary electron sink in photosynthesis and, in turn, recover others F., e.g. NADF-N-reductase. In photosynthetic systems of a flavodoksina fer-redoksinam are replaced (see Photosynthesis).

Considerable group F. make flavin monooxygenases (hydroxylases, oxidases with the mixed functions). Effect of many enzymes of this group, apparently, includes consecutive reduction stages of flavin in the dihydroform recovering oxygen to hydrogen peroxide (see Peroxides), and then enzyme — flavin — a peroksidazny complex hydroxylates substrate. The majority of these monooxygenases functions with NAD-N or NADF-N. Substrate of a hydroxylation is a positive effector for recovery of flavin a pyridinic nucleotide therefore enzyme functions only in the presence of enough substrate. Mick-rosomnye the hydroxylating enzymes containing R-450 cytochrome function thanks to the recovery which is carried out by a yellow enzyme R-450 cytochrome — reductase, edges are catalyzed by electron transfer from NADF-N to R-450 cytochrome.

Bibliography: Dickson M. and Webb E. Enzymes, the lane with English, t. 2, page 679, etc., M., 1982; Whyte A. and d river. Fundamentals of biochemistry, the lane with English, t. 1, page 397, etc., M., 1981; Flavins and flavoproteins, ed. by E. Page of Slater, Amsterdam — N. Y., 1966;

Warburg O. H. u. Christian W. Ueber ein neues Oxydationferment und sein Absorptionsspektrum, Biochem. Z.,

Bd 254, S. 438, 1932. H. V. Gulyaeva.

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