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Lecture 6 Vitamins and Coenzymes

Lecture 6 Vitamins and Coenzymes. Outline. Classification of vitamins Structure of vitamins Features and functions of vitamins as coenzyme. Introduction. Some enzymes require cofactors for activity -- Essential ions mostly metal ions : Zn 2+ ,Fe 2+

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Lecture 6 Vitamins and Coenzymes

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  1. Lecture 6Vitamins andCoenzymes

  2. Outline • Classification of vitamins • Structure of vitamins • Features and functions of vitamins as coenzyme

  3. Introduction • Some enzymes requirecofactorsfor activity • --Essential ions • mostly metal ions: Zn2+,Fe2+ • -- Coenzymes(organic compounds) • Vitamin-derived coenzymes-derivatives of vitamins.

  4. Vitamins Definition：Vitamins are organic nutrients that are required in small quantities for a variety of biochemical functions and which, generally, cannot be synthesized by the body and must therefore be supplied by the diet.

  5. History • Thiamine was discovered in 1912 & was thought to be a vital amine compound & thus the term vitamin was invented • Vita=vital for life • Min=amine

  6. Properties • Vital to life; are essential • Organic compounds • Individual units; not linked in chains • Do not provide energy • Assist with release of energy (coenzymes) • Needed in small amounts: micro/milli grams • Fruits and vegetables are a primary source

  7. Nomenclature and function • Vitamin A: prevent night blindness • Vitamin B: anti-beriberi factor • Vitamin C: anti-scurvy factor • Vitamin D: anti-ricket factor • Vitamin E: for reproduce properly • Vitamin K: concerned with coagulation

  8. Water Soluble Vitamin C B Vitamins Thiamine (B1) Riboflavin (B2) Niacin Pantothenic Acid Biotin Pyridoxine (B6) Folic Acid Vitamin B12 (cyanocobalamin) Lipid Soluble Vitamin A Vitamin D Vitamin E Vitamin K Classification Energy-releasing Hematopoietic

  9. Water-soluble vitamins Common features: 1.Water soluble 2.Easy to be discharged through urine. Rarely accumulated to the toxic concentrations. 3.Their storage is limit. Must be provided regularly. Vitamin B12 is the only water-soluble vitamin that can be stored in the liver for many years.

  10. B Vitamins Thiamin (B1) Riboflavin (B2) Niacin Pantothenic Acid Biotin Vitamin B6 Folic Acid Vitamin B12 • Indispensable for metabolism. • B vitamins help the body to produce energy. • B complex vitamin are necessary for healthy skin, hair, eyes and liver, also help the nervous system function properly.

  11. 1. Vitamin B1 (Thiamine ) • In 1897 Christiaan Eijkman discovered that fowl fed on a diet of cooked, polished rice developed paralysis, which could be reversed by discontinuing rice polishing. • He attributed that to a nerve poison in the endosperm of rice, from which the outer layers of the grain gave protection to the body. • Eijkman was awarded the Nobel Prize in Physiology and Medicine in 1929, because his observations led to the discovery of vitamins.

  12. Thiazole ring Thiamine: named as the "thio-vitamine" ("sulfur-containing vitamin") Pyrimidine ring Active form :Thiamine pyrophosphate (TPP or cocarboxylase) Reactive carbon atom

  13. Biochemical function ﹡TPP: • co-enzyme of oxidative decarboxylation of α–keto acids and transketolase, involved in carbohydrate metabolism. ﹡with effects in the nerve conduction, inhibiting the cholinesterase activity.

  14. Food Sources of thiamin • Recommended Dietary Allowance(RDA): • M:1.2mg/d， F:1.1mg/d • Most exceed RDA in diet • Surplus is rapidly lost in urine; non toxic • Sources • Unrefined cereal grains and meat；seeds, nuts, legumes

  15. Deficiency of Thiamin • Thiamine was named "the anti-beriberi factor ”(or antineuritic vitamin) (1926) • Beriberi: • The word is from a Sinhalese phrase meaning "I cannot, I cannot", the word being doubled for emphasis. • a neurological and cardiovascular disease • Weakness, nerve degeneration, irritability, poor arm/leg coordination, loss of nerve transmission, edema, heart failure.

  16. Beriberi

  17. 2. Vitamin B2 (riboflavin) • Vitamin B2, also commonly called riboflavin, gets its name from its color. The root of this word is the Latin word "flavus" meaning "yellow."

  18. Active form (coenzyme): • flavin mononucleotide (FMN) • flavin adenine dinucleotide (FAD) Ⅲ Ⅱ Ⅰ Vit B2 FMN AMP FAD

  19. Biochemical function • FMN and FAD are the prosthetic group of oxidoreductases with function of transmitting hydrogen, they playkey roles in energy metabolism. • Proteins with FAD or FMN attached to them are often referred to as flavoproteins.

  20. Food Sources of riboflavin • Adequate amounts of B2 is present in eggs, milk, meat & cereals. • Destroyed by ultraviolet light & irradiation • RDA：M: 1.4mg/d， • F: 1.2mg/d

  21. Deficiency Symptoms associated with riboflavin deficiency include • Glossitis（舌炎） • Seborrhea（皮脂溢出） • Angular stomatitis（口角炎） • Cheilosis（唇干裂） • Scrotitis（阴囊焱） • Photophobia（畏光） • uncommon

  22. 3. Vitamin PP(niacin, pellagra preventive factor) Pyridine derivative ﹡ Vitamin PP nicotinic acid nicotinamide • The name 'niacin' was derived from “nicotinic acid + vitamin” ﹡Active form (coenzyme) Nicotinamide adenine dinucleotide(NAD+) Nicotinamide adenine dinucleotide phosphate(NADP+)

  23. nicotinamide adenine NAD+ (Nicotinamide adenine dinucleotide), R: H NADP+ (Nicotinamide adenine dinucleotide phosphate),R:

  24. Biochemical function • ﹡NAD+ and NADP+: coenzyme of dehydrogenases, transfer of hydrogen.

  25. Food Sources of Vit PP and Deficiency • Food Sources • Niacin is found in unrefined and enriched grains and cereal,milk,and lean meats, especially liver. Limited quantities of niacin can also be obtained from the metabolism of tryptophan. • Deficiency • Pellagra(Italian:rough skin) • Symptoms: three Ds: dermatitis（皮炎）, diarrhea（腹泻）, dementia（痴呆）, if not treated may rarely lead to death (4th D) • Mostly seen among people whose staple diet is corn or maize.

  26. 4.Pantothenic acid • Its name is derived from the Greek “pantothen” meaning "everywhere“. • It is found in numerous foods and also is synthesized by intestinal bacteria. pantoic acid b-alanine

  27. Active form : • coenzyme A (CoA) • 4-phosphopantetheinyl: acyl carrier protein (ACP) • Biochemical function • ﹡CoA and ACP are coenzyme of acyl transferase，transfer of acyl. Pantothenic acid

  28. 5. Biotin (anti-egg white injury factor) • The name biotin is taken from the Greek word  bios  meaning "life." • It is necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids. Imidazole ring Thiophene ring

  29. Biochemical function • Biotin is covalently bound to the ε-amino groups of lysine residues of biotin-dependent enzymes. • Biotin: co-enzyme of carboxylase, the carrier of activated carbon dioxide(CO2).

  30. Biotin - Food Sources • Widespread in food • Cheese, egg yolk, liver, peanut butter, soybeans, fish • Synthesized by GI (gastrointestinal ) bacteria.

  31. Biotin Defficiency • Avidin was first isolated from raw chicken egg white by Esmond Emerson Snell • Deficiency: rare • Depression • Numbness（麻痹） • Lethargy • Dermatitis（皮炎） • Did You Know? • Eating large amounts of raw egg white can lead to biotin deficiency • Raw egg whites contain a glycoprotein (Avidin) which tightly binds biotin and prevents its absorption from the intestine; cooking denatures protein.

  32. 6. Vitamin B6 (pyridine derivatives) ﹡Three forms of vitamin B6: • Pyridoxine, pyridoxal, pyridoxamine

  33. ﹡Active form : • Pyridoxal-Phosphate(PLP), pyridoxamine-Phosphate • Biochemical function ﹡Coenzyme of amino acid aminotransferase, decarboxylase, and -amino-- levulinate synthase （ALA synthase）

  34. Food Sources of Vit B6 • Most protein-rich foods • such as meat, fish, and • poultry provide ample • vitamin B6 ; some • vegetables and fruits • are good sources, too.

  35. Vitamin B6 Deficiency • Overt deficiencies are rare • Isoniazid therapy (the first-line antituberculosis medication) can induce VitB6 deficiency. • Manifestations • Stomatitis, glossitis • Dermatitis • Irritability, confusion, depression • Anemia

  36. 7. Folic acid (or folate) • Folic acid or folate derive their names from the Latin word folium (which means "leaf"). • Obtained from yeasts and leafy vegetables as well as animal liver. ﹡Active form: Tetrahydrofolate (THF or FH4)

  37. pteridine para-aminobenzoic acid (PABA) glutamic acid FH4 (or THF)

  38. Biochemical function • FH4 : coenzyme of transferase of one carbon unit. The N5 and N10 of FH4 participate in the transfer of one carbon units. N5—CH3—FH4 N5、N10—CH2—FH4 N5、N10=CH—FH4 N10—CHO—FH4 N5—CH=NH—FH4

  39. Major Functions • New cell synthesis - GI tract, RBC • Protein synthesis • DNA/RNA synthesis • Increased needs w/ pregnancy • It is especially important during periods of rapid cell division and growth.

  40. Folic Acid - Food Sources • “Foliage” - green leafy vegetables, legumes, organ meats, orange juice, sunflower seeds, fortified grains. • Can be destroyed by heat and oxygen

  41. Folic Acid - Deficiency • Megaloblastic anemia (macrocytic anemia) • An anemia (of macrocytic classification) that results from inhibition of DNA synthesis in red blood cell production. • This is often due to deficiency of vitamin B12 and/or folic acid. • Pregnant or lactating women may require folic acid supplementation. • Folic acid deficiency in pregnant women may cause neural defects in the fetus.

  42. Megaloblastic Anemia

  43. Dimethylbenzimidazole(DMB) • It is the most complicated vitamin and contains the biochemically rare element cobalt. Active form: Methylcobalamin; 5 -deoxyadenosylcobalamin 8. Vitamin B12 (cobalamin, anti-pernicious anemia vitamin) (R：-CH3) (R：5`-deoxyadenosine) Corrin ring

  44. Biochemical function and deficiency ﹡Biochemical function ：methyl transfer ﹡Deficiency：,Megaloblastic anemia (pernicious anemia), nerve disease , high blood level of homocysteine.

  45. Food Sources of Vitamin B12 • Vitamin B12 is a unique vitamin, synthesized by only microorganisms and not by animals and plants. • It is naturally found in meat (especially liver and shellfish), milk and eggs. Animals, in turn, must obtain it directly or indirectly from bacteria.

  46. Causes of Vitamin B12 Deficiency • Vitamin B12 deficiency is rarely due to an absense of the vitamin in the diet. • It is much more common in patients who fail to absorb the vitamin from the intestine, resulting in pernicious anemia. • Lack of intrinsic factor (IF)

  47. Pernicious Anemia(PA) • The classic description of patient with PA • Lemon colored skin (anemia/icterus) • Shiny tongue (atrophic glossitis) • Mentally sluggish • Shuffling broad gait

  48. B Vitamins Coenzyme Roles Coenzyme TPP FAD FMN NAD NADP PLP THF CoA Biotin B12 Protein Metabolism Carbohydrate Met Fat Metabolism NAD PLP PLP TPP FAD FMN NADP FAD FMN NAD B12 B12 B12 B12 THF NAD CoA Biotin CoA E N E R G Y • Thiamin • Riboflavin • Niacin • B6 • Folate Pantothenic Acid • Biotin B12 Vitamin

  49. 9. Vitamin C（ascorbic acid） • Water soluble • sour taste (acid) • Six-carbon polyhydroxy compound • Strong antioxidant

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