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4. Alikulov Z. and Schieman. 1985. Presence of active molybdenum cofactor in dry seeds of wheat and barley. Plant Sci. 40: 161-165.
5. Kawakami N, Miyake Y. and N. Kzuhiko. 1997. ABA insensitivity and low ABA levels during seed development of non-dormant wheat mutants. J.Exp. Botany. 48(312): 1415-1421.
6. Finch-Savage W.E.; Cadman C.S.C.; Toorop P.E.; Lynn J.R.; Hilhorst H.W.M. Seed dormancy release in Arabidopsis Cvi by dry after-ripening, low temperature, nitrate and light shows common quantitative patterns of gene expression directed by environmentally specific sensing. Plant Journal, v.51, p.60-78, 2007.
© Z. Alikulov, A. Shukhatova, G. Shalakhmetova, 2015
УДК 2788
Alikulov Z.
Associate Professor, Department of Microbiology and Biotechnology of the Eurasian National University. L.N.Gumilev E-mail: [email protected] Talapova Zh., Dyussembayev K.
Undergraduate of the Eurasian National University. L.N.Gumilev E-mail: [email protected]
ROLE OF ANIMAL MOLYBDOENZYMES IN DETOXIFICATION OF XENOBIOTICS
Abstract
In animals xanthine oxidase (XO) and aldehyde oxidase (AO) are closely related enzymes with similar molecular properties but differ somewhat in substrate specifity; they catalyze the oxidation of a wide range of heterocyclic compounds containing nitrogen atoms. Unlike membrane-bound cytochrome P450 monooxygenases, XO and AO are cytosolic and stable during the oxidative stress (lipid peroxidation). The review considers that the activities of these enzymes can be regulated by administration with molybdenum (activation) and its deficiency may cause oncological diseases.
Xenobiotic-transforming enzymes. Most the attention to date in metabolism of drugs and foreign compounds has been focused on the microsomal cytochrome P450 (CYP) enzyme family or monooxygenase system. This membrane bound system plays an important role in the oxidation of aromatic carbocyclic compounds in animals and human. However, the presence of the one or more nitrogen atoms in the aromatic rings makes heterocyclic compounds also susceptible to oxidation via a second group of enzymes known as the "molybdenum hydroxylases". These cytosolic enzymes, which include xanthine oxidase aldehyde oxidase (AO, EC 1.2.3.1) and (XO, EC 1.2.3.2) form a closely related group with similar molecular properties but differ somewhat in substrate specificity [1].
These enzymes catalyze both oxidation and reduction of a broad range of drugs and other xenobiotics indicating the importance of these enzymes in drug oxidation, detoxification and activation. Xanthine oxidoreductase (XOR) appears in two interconvertible forms xanthine dehydrogenase (XDH), and xanthine oxidase (XO). Xanthine oxidoreductase catalyzes the hydroxylation of hypoxanthine to xanthine and of xanthine to urate. XDH reduces NAD+, but XO reduces molecular oxygen at the flavin center. Molybdenum-containing hydroxylases catalyze the hydroxylation of carbon centers using oxygen derived ultimately from water, rather than O2, as the source of the oxygen atom incorporated into the product, and do not require an external source of reducing equivalents [1].
The relative importance of these two groups of oxidative enzymes is illustrated by comparing the in vitro oxidation of several bicyclic ring system. Naphtalene is oxidized via the CYP P450 system to an unstable epoxide intermediate which ultimately gives rise to a mixture of 1-naphtol and 2-naphtol. However, naphthalene is not a substrate for the molybdenum hydroxylases. Quinoline, 1-azanaphtalene, reacts not only with the CYP P450 system but also with aldehyde oxidase to give a number of mono- and dihydroquinolines with rabbit or rat liver fractions.
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As the number of N atoms in the molecule increases, the molybdenum hydroxylases play a more dominant role in the oxidative biotransformation of these compounds. Thus, quinazoline, 1,3-diazanaphtalene, is rapidly oxidized by both aldehyde oxidase and xanthine oxidase to quinazolin-4-one, whereas only small amounts of phenolic P450 products can be detected. Furthermore, quinazolin-4-one is subsequently converted to quinazolin-2,4-dione by the molybdenum hydroxylases. Finally pteridine, 1,3,5,8-tetraazanaphtalene, is oxidized in vitro via the molybdenum hydroxylases only; xanthine oxidase converts it sequentially to pteridin-2,4,7-trione, whereas it is converted to pteridin-2,4-dione by aldehyde oxidase [1].
The reason for the change in emphasis from microsomal oxidation of naphthalene to the molybdenum hydroxylase catalyzed attack of pteridine is due to the additive activating effect of each nitrogen atom toward nucleophilic attack of the ring system. The molybdenum hydroxylases catalyze a reaction which involves attack by a nucleophile. Therefore, oxidation normally occurs at the carbon atom adjacent to ring nitrogen, which is generally the most electropositive carbon. The oxygen atom incorporated into the substrate is ultimately derived from water. In contrast, the CYP P450 system catalyzes electrophilic attack involving molecular oxygen, and the carbons in the heterocyclic rings are deactivated toward electrophilic reagents. The two reactions can be presented thus [1]:
RH + OH- ^ aldehyde oxidase, xanthine oxidase ^ ROH + 2e- + H+
RH + O2 + NADPH + H+ ^ CYP P450 enzymes ^ ROH + H2O + NADP+
The molybdenum hydroxylases function by being alternately reduced by the substrate (RH) and reoxidized by molecular oxygen (or NAD+) under physiological conditions. Both superoxide anion and hydrogen peroxide are produced via either one-electron or two-electron transfer. These pathways can be illustrated by the following equation:
FADH2 + 2O2 ^ FAD + 2H+ + 2O2-
FADH2 + O2 ^ FAD + H2O2
Reactions catalyzed by molybdoenzymes. AO and XO oxidize the oxidation of a wide range of heterocyclic compounds. Although the enzymes have similar molecular properties, their substrate specificities are quite different, with regard to both rate of oxidation and the position of attack. However, the role of these enzymes in the oxidation of drug-derived aldehydes has not been established. The investigation described the interaction of eleven structurally related benzaldehydes with guinea pig liver AO and bovine milk XO, since they have similar substrate specificity to human molybdenum hydroxylases. The compounds under test included mono-hydroxy and mono-methoxy benzaldehydes as well as 3,4-dihydroxy-, 3-hydroxy-4-methoxy-,4-hydroxy-3-methoxy-, and 3,4-dimethoxy-benzaldehydes. In addition, various amines and catechols were tested with the molybdenum hydroxylases as inhibitors of benzaldehyde oxidation. The kinetic constants have shown that hydroxy-, and methoxy-benzaldehydes are excellent substrates for AO with lower affinities for XO. Therefore, AO activity may be a significant factor in the oxidation of the aromatic aldehydes generated from amines and alkyl benzenes during drug metabolism. In addition, amines acted as weak inhibitors, whereas catechols had a more pronounced inhibitory effect on the AO activity. It is therefore possible that AO may be critical in the oxidation of the analogous phenyl acetaldehydes derived from dopamine and noradrenaline.
There are very few monocyclic substrates of these enzymes; pyridine and its diaza analogues, pyrimidine, pyrazine and pyridazine, do not react with the molybdoenzymes in vitro. However, some substituted pyridines and pyrimidines are metabolized, and these examples emphasize the difference in substrate specificity between the AO and XO [1].
It was for the first time found that highly purified milk XO may convert nitrate to nitrite [1]. Later Millar and co-workers showed that XO catalyses nitrate and nitrite reduction to nitric oxide under anaerobic conditions [3]. The XO reducing substrate xanthine, NADH, triggered nitrate or nitrite reduction to NO, and the molybdenum-binding XO inhibitor - oxypurinol prevents this NO formation, indicating that nitrate (nitrite) reduction occurs at the molybdenum site. Nitrite and reducing substrate concentrations were important regulators of XO-catalyzed NO generation [3]. It is well known that in mammals including humans, NO is an important cellular signaling molecule involved in many physiological and pathological processes.
The detailed studies comparing the occurrence of AO and XO in more than 100 species have shown that these enzymes are present, either separately or together, in species as diverse as the sea anemone and man. Species differences in the levels of AO are more pronounced than those of XO, with herbivores containing the highest levels of former enzyme. Levels of both enzymes are high in mammalian liver although xanthine oxidase is present in
similar concentrations in lactating mammary tissue and small intestine, and concentrated 1000-fold in bovine milk lipid globules [3].
Sulfite oxidase, (EC 1.8.3.1) third molybdoenzyme is an enzyme in the mitochondria of all eukaryotes. It oxidizes sulfite to sulfate and, via cytochrome c, transfers the electrons produced to the electron transport chain, allowing generation of ATP in oxidative phosphorylation [1].
The recently discovered mammalian fourth molybdenum containing protein mARC1 is capable of reducing N-hydroxylated compounds. It was named mARC because the N-reduction of amidoxime structures was initially studied using this isolated mitochondrial enzyme. Upon reconstitution with cytochrome b(5) and b5 reductase, benzamidoxime, pentamidine, and diminazene amidoximes, N-hydroxymelagatran, guanoxabenz, and N-hydroxydebrisoquine are efficiently reduced. These substances are amidoxime/N-hydroxyguanidine prodrugs, leading to improved bioavailability compared to the active amidines/guanidines. Thus, the recombinant enzyme allows prediction about in vivo reduction of N-hydroxylated prodrugs. Furthermore, the prodrug principle is not dependent on cytochrome P450 enzymes [4]. mARC and its N-reductive enzyme system plays a major role in drug metabolism, especially in the activation of so-called "amidoxime-prodrugs" and in the detoxification of N-hydroxylated xenobiotics, though its physiological relevance is largely unknown [4].
Molybdenum deficiency. At least 50 molybdenum-containing enzymes are now known in bacteria, plants and animals. Therefore, molybdenum is an essential trace element for virtually all life forms. It functions as a cofactor for a number of enzymes that catalyze important chemical transformations in the global carbon, nitrogen, and sulfur cycles.
It has been claimed that molybdenum status influences susceptibility to certain forms of cancer and that the high incidence of esophageal cancer among the Bantu in Transkei (South Africa) is associated with a deficiency of this element in locally available food. Studies in Henan province, China, suggest that a high incidence of esophageal cancer is associated with lower than normal contents of molybdenum in drinking water and food as well as in serum, hair and urine [5]. Esophageal cancer tissue also had lower molybdenum content than normal. It may well be relevant that inclusion of 2 or 20 ^g of molybdenum/g in the diet of rats has been found to inhibit esophageal and stomach cancer following the administration of N-nitrososarcosine ethyl ester, a nitrosamine. Molybdenum in the drinking water of rats at a concentration of 10 mg/l inhibited mammary carcinogenesis induced by N-nitroso-N-methylurea [6].
Thus, plants are common sources of molybdenum for animals and human. Plants require molybdenum to synthesize nitrate reductase, a molybdoenzyme necessary for converting nitrates from the soil to amino acids. When soil molybdenum content is low, plant conversion of nitrates to nitrosamines increases, resulting in increased nitrosamine exposure for those who consume the plants. References
1. Beedham C. Molybdenum hydroxylases. In: "Enzyme systems that metabolize drug and xenobiotics" Ed. Costas Ioannidis. 2001. John Wiley & Sons Ltd. 146-188.
2. Alikulov, Z. A.; L'Vov N, P.; Kretovich, V. L. 1980. Nitrate and nitrite reductase activity of milk xanthine oxidase. Biokhimiia. 45:1714-1718. (1980).
3. Millar T.M., Stevens C.R., Benjamin N., Eisenthal R., Harrison R., Blake D.R. 1998. Xanthine oxidoreductase catalyzes the reduction of nitrates and nitrite to nitric oxide under hypoxic conditions. FEBS Letters. 427: 225-228.
4. Grunewald, S., Wahl, B., Bittner, F., Hungeling, H., Kanzow, S., Kotthaus, J., Schwering, U., Mendel. R.R., and B. Clement. 2009. The fourth molybdenum containing human enzyme mARC: cloning and reduction of N-dydroxylated structures. J. Med. Chem. 51, 8173 - 8177.
5. Seaborn C.D, Yang S.P. 1993. Effect of molybdenum supplementation on N-nitroso-N-methylurea-induced mammary carcinogenesis and molybdenum excretion in rats. Biol Trace Elem Res 39(2-3):245-256.
6. Brewer G.J, Dick R.D, Grover D.K. 2000. Treatment of metastatic cancer with tetrathiomolybdate, an anticopper, antiangiogenic agent: Phase I study. Clin Cancer Res. 6:1-10.
© Z. Alikulov, Zh. Talapova, K. Dyussembayev, 2015
Международный научный журнал «СИМВОЛ НАУКИ»_№4/2015_ISSN 2410-700X
ИСКУССТВОВЕДЕНИЕ
УДК 7
Папшева Любовь Владимировна
доцент кафедры дизайна ИСТиД СКФУ, г.Пятигорск, РФ
РИСУНОК В ДИЗАЙНЕ СРЕДЫ Аннотация
Статья посвящена методу обучения, которая позволяет достичь наилучших результатов в понимании объема и формы предмета и передачи их в пространстве.
Ключевые слова
рисунок, методика, дизайн среды, объемно-пространственное мышление.
Рисунок в дизайне среды является одной из основных дисциплин т. к. он в сочетании с другими предметами начертательной геометрией, скульптурой, и др. развивает объемно-пространственное мышление, учит правильно видеть объемную форму предмета и последовательно, передавать на плоскости листа.
Эволюция рисунка на современном этапе показала, что самым продуктивным методом рисования является - геометральный - сопоставление натурных форм с простейшими геометрическими телами (куб, цилиндр, конус и т.д.).
Именно этот метод обучения позволяет достичь наилучших результатов в понимании объема и формы предмета и передачи их в пространстве.
Процесс учебного рисунка включает в себя такие разделы как: перспектива, законы света и тени, пластическая анатомия и пропорции.
Работа должна идти» от простого к сложному».
На первом курсе студенты овладевают линейно- конструктивным построением (с учетом перспективы и пропорций) простых геометрических тел.
студентам предлагаются задания на построение геометрических тел по отношению к линии горизонта: выше линии горизонта, ниже линии горизонта и на линии горизонта).
Нахождение геометрических тел относительно друг друга в пространстве.
На первых порах нет необходимости в тональном рисунке, нужно научиться владеть линией, передавать объем толщиной линий.
Первый план - линии более интенсивные, задний план- нажим на карандаш ослабевает. Невидимые плоскости передавать чуть заметными линиями. Обычно постановка условно делится на три плана. Прорабатывают как правила 2 план, задний план как я уже говорила тон нужно ослабить, а вот на первом плане, наоборот выполнить линии более активно, смягчая к краям работы (к краям планшета).
Предметы строятся, как будто они прозрачные, строятся и невидимые плоскости.
Только так мы сможем научиться передавать объем предмета - который имеет три величины: высоту, ширину и длину и ограничивается в пространстве различными плоскостями.
Задача студентов в совершенстве овладеть линией при построении объемов, а также в совершенстве овладеть одним из наиважнейших разделов рисунка - перспективой линейной и воздушной.
При выполнении рисунков простых геометрических тел необходимо постоянно проводить параллели, указывать на связь этих гипсовых форм с формой архитектурных объектов.
Дом похож на куб или на четырехгранную призму - значит все законы построения куба, четырехгранной призмы или др. геометрических тел точно также работают в рисунке с натуры здания или др. архитектурного объекта.
При внимательном анализе любого архитектурного средового объекта, любую сложную форму можно разложить на простые геометрические тела.
Формы могут врезаться или плавно переходить одна в другую.
Поэтому на следующем этапе работы, после освоения построения простых геометрических тел необходимо перейти к построению врезок.
