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Metabolism of Vitamins Metabolism of vitamins Arash Azarfar Lorestan University McDowell, L. R. 2000. Vitamins in Animal and Human Nutrition, 2nd ed., Iowa State University Press, Ames, IA Bender, 2003, Nutritional biochemistry of vitamins, 2nd edition, Cambridge, UK. Berdanier,C.D. 2000, Advanced nutrition micronutrients, CRC Press. Lorestan University ویتامین ها Vitamins Vitamins are substances which are involved in: • Gene expression (A, D, B1, B12) • Structural role in visual pigments (A as retinol) • As antioxidant (A, E, C) • As enzyme cofactors (B group, K) The first identified vitamin was identified by Funk(1921). ‘Vital amine’ or ;vitamine’ ‘Vitamin’ Lorestan University ویتامین ها : Vitamin : fat soluble type Names Functions A, retinoic acid, retinol, Vision, retinaldehyde Maintenance of epithelial cells Reproduction, Growth, D, Phosphocalcium metabolism, cholecalciferol,ergocalciferol Growth, Reproduction, E, α-, β-, γ-, tocopherols Biological antioxidant, phospholipids' membrane stability, Immunomodulation K, menadion, phylloquinone, Cofactor in coagulation menaquinone Lorestan University ویتامین ها Vitamins: water soluble Names Functions Thiamin, B1, aneurin Coenzyme in oxidative Decarboxylation, Role in neurophysiology Ribofelavin, B2 Intermediary in the transfer of electrons in biological oxidation- reduction reactions Niacin , B3, nicotinamide, pp Constituent of coenzyme NAD factor and NADP in carbohydrate, protein and fat metabolism Panthotenic acid, B5 Coenzyme A precursor B6, pyridoxine, pyridoxal, Amino acid metabolism, pyridoxamine Formation of biogenic amines Lorestan University Vitamins: water soluble Names Functions Biotin , B7, H, coenzyme R Coenzyme in carbohydrate, protein and fat metabolism Folate, B9, B11, Bc, M , folic acid Growth,Haematopoiesis, Maintenance of immune system B12, Integrity of nervous system, cyanocobalamin,aquacobalamin Growth, Haematopoiesis Choline Synthesis of acetylcholine,component of phospholipids, metyle radical donor, lipotrophic factor Lipoic acid, thioctic acid C, ascorbic acid, dehydroascorbic Collagen biosynthesis, Transfer of acid electrons, Oxidation reaction Lorestan University Thiamin, B1 Lorestan University Overview, History of B1 In 1630, Jacobus Bonitus, first record of disease in Java named Beriberi. In 1894, Takaki, a surgeon in the japanese naavey, suggested that the disease was diet related. 1890 , Eijkman observed a beriberi-like condition (polyneuritis) in chicken. 1906, Jansen and 1926 (Funk) reported isolation of a material from rice polished which cured Beriberi. Jansen named the material aneuria. Vitamin B1, oryzamin, polyneuramin, vitamin F, antineuritic vitamin and antiberiberi vitamin. In 1936 Thiamin was synthesized by Williams. Lorestan University Structure of Thiamin, B1 • Named thiamin because it has both sulfur and amine group. Lorestan University Source of Thiamin, B1 Sources of thiamin: Thiamin is widely distributed in the food supply even though some food had virtually no thiamin, polished rice, fats, oils, refined sugar, and unenriched flours are in this group. Peas and other legumes seeds and soybean meal are good sources. the amount of thiamin increases with the maturity of the seed. Whole-grain and cereal by products contain nutritionally significant amounts of thiamin. Dried brewer’s yeast and wheat germ are both rich in thiamin. Lorestan University Metabolism of B1 Dietary thiamin phosphates are hydrolyzed by intestinal phosphatases, and the resultant free thiamin is absorbed by active transport in the duodenum and proximal jejunum, with little absorption in the rest of the small intestine. Thiamin active transport is sodium-independent and requires an outwardly directed proton gradient (i.e., it is dependent on a proton-pumping ATPase). Antimetabolites, such as pyrithiamin, compete with thiamin for active transport. The transport system is saturated at relatively low concentrations of thiamin (about 2 µmol per L), thus limiting the amount of thiamin that can be absorbed. Lorestan University Metabolism of B1 Both free thiamin and thiamin monophosphate circulate in plasma; about 60% of the total is the monophosphate. Under normal conditions, most is bound to albumin; when the albumin binding capacity is saturated, the excess is rapidly filtered at the glomerulus and excreted in the urine. Although a significant amount of newly absorbed thiamin is phosphorylated in the liver, all tissues can take up both thiamin and thiamin monophosphate, and are able to phosphorylate them to thiamin diphosphate and thiamin triphosphate. Lorestan University Metabolism of B1 2-3% of the thiamin in nervous tissue is present as the triphosphate, which also occurs in significant amounts in skeletal muscle. In the nervous system, the triphosphate is found exclusively in the membrane fraction; muscle thiamin triphosphate is mainly cytosolic. There are two pathways for formation of thiamin triphosphate from the diphosphate: 1. Phosphorylation by ATP, catalyzed by thiamin diphosphate kinase, which acts only on protein-bound thiamin diphosphate 2. Phosphorylation by ADP, catalyzed by adenylate kinase Lorestan University Thiamin antagonist There are two analogs of thiamin: 1-oxythiamin (an analog having the C-4 amino group replaced by a hydroxyl group) 2- pyrithiamin (a compound with the thiazole ring replaced by a pyridine). Mechanisms of action: Oxythiamin is readily converted to the pyrophosphate and competes with thiamin for its place in the TPP-enzyme systems. Oxythiamin depresses appetite, growth, and weight gain and produces bradycardia, heart enlargement, and an increase in blood pyruvate, but it does not produce neurological symptoms. Pyrithiamin prevents the conversion of thiamin to TPP by interfering with the activity of thiamin kinase. Pyrithiamin results in a loss of thiamin from tissues, bradycardia, and heart enlargement, but does not produce an increase in blood pyruvate. 3-amprolin, Amprolium inhibits the absorption of thiamin from the intestine and blocks the phosphorylation of the vitamin. Lorestan University Thiaminases a natural antagonist A type of natural antagonist is a group of enzyme called thiaminases. The enzyme has several forms and has been found in fish, shellfish, ferns, betel nuts, and a variety of vegetables. Antithiamin substances found in tea and other plant foods inactivate the vitamin. Tannic acid is one such substance; another is caffeic acid (3,4-dihydroxycinnamic acid). Some of the flavinoids and some of the dihydroxy derivatives of tyrosine have antithiamin activity. Lorestan University Metabolic functions of Thiamin, B1 1- important coenzyme in several energy metabolism pathways. Thiamin is a part of the coenzyme thiamin pyrophosphate (TPP) (thiamin with two molecules of phosphate attached to it), also known as co-carboxylase, which is required in the metabolism of carbohydrates. Thiamin is also active in the decarboxylation of α-ketoglutaric acid to succinyl CoA in the citric acid cycle. 2- role in nerve and brain function (Combs,1992). In addition to its role as a coenzyme, it is speculated that thiamin has an independent role in neural tissue since it has been shown that stimulation of nerve fibers results in release of free thiamin and thiamin monophosphate. If a neurophysiologically active form of thiamin exists, it is as thiamin triphosphate. Lorestan University Ruminants and Thiamin, B1 Amounts of thiamin synthesized daily in the rumen (28to72mg) have been reported to equal or exceed dietary intake (Brevesetal.,1981). Thiamin is generally non toxic as the upper safe feeding level for most non ruminants is 1,000 times the requirement (NRC, 1987) Lorestan University Deficiencies of Thiamin, B1 The biological half-life of thiamin is 10 to 20 days, and deficiency signs can develop rapidly during depletion. 1-when thiaminases associated with feeds (Bracken ferns and some raw fish products , Feeding diets high in sulphate) 2-thiaminase produced from altered ruminal fermentation (feeding diets rich in concentrate which cause a sudden drop in ruminal pH) Deficiencies of thiamin block several of the energy producing Krebs cycle reactions. Deficiency of thiamin results in a central nervous system disorder. Polioencephalomalacia (PEM), is the most common thiamin deficiency disorder. Symptoms of PEM include a profuse, but transient diarrhea, listlessness, circling movements, opisthotonus (head drawn back over neck), and muscle tremors. If treated promptly by parenteral injection of thiamin (2.2mg/kg of body weight), the condition can be reversed (NRC,1996). Lorestan University • کمبود: دستگاه عصبی و قلب به خاط متابولیسم هوازی شان به کمبود آن حساسند. طیور: ستاره نگری stargrazing طیور بالغ بعد از سه هفته و جوجه ها بعد از 2 هفته عﻻئم کمبود را نشان می دهند. پاسخ به درمان خیلی سریع است)چند ساعت.( نشخوارکنندگان: پلی انسفالوماﻻسیا )PEM عﻻئم: اسهاال زیاد در مدت کوتاه، خستگی، حرکات دوار، ستاره نگری و تومورهای عضﻻنی علت: مصرف خوراک با کربوهیدرات محلول زیادکه منجر به رشد بیش از حد باکتریهای تولیدکننده تیامیناز میشود و جیره های حاوی سولفات زیاد Lorestan University Lorestan University Dietary recommendation of B1 • Monogasteric The thiamin needs of an individual are influenced by age, energy intake, carbohydrate intake, and body weight. 0.5 mg/1000 kcal (4184 kJ). • Ruminants Amounts of thiamin synthesized daily in the rumen (28to72mg) have been reported to equal or exceed dietary intake (Brevesetal.,1981). High carbohydrated diet and high sulfur diet Lorestan University Riboflavin, B2 Lorestan University ریبو فﻻوین یک ماده زرد رنگ پرتغالی است . منابع :
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