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Chapter 06 Vitamins and Coenzymes 维生素与辅酶

Chapter 06 Vitamins and Coenzymes 维生素与辅酶. 1. Vitamins. 1.1 What are vitamins?

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Chapter 06 Vitamins and Coenzymes 维生素与辅酶

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  1. Chapter 06 Vitamins and Coenzymes 维生素与辅酶

  2. 1. Vitamins 1.1 What are vitamins? Vitamins are the organic compounds which play important roles in metabolism (mostly as coenzymes) but could not be synthesized by human (or animal) body itself. In principle, plants can synthesize all the vitamins they need.

  3. 1.2 Classification of vitamins 1.2.1 Water-soluble vitamins: vitamin B group―B1, B2, PP, B6, B12 vitamin PP, pantothenic acid, biotin, Folic acid, vitamin C.  1. 2.2 Fat-soluble vitamins: vitamin A, D, E and K

  4. 2. Vitamins and coenzymes • Some vitamins are the coenzymes independently. • Some vitamins are components of coenzymes.

  5. Key soluble vitamins, their corresponding coenzymes and functions • Vitamin Coenzyme Function • B1(Thiamine) TPP(Thiamine pyrophosphate) Transfer of aldehyde group, • decarboxylation of α-keto acid • B2(Riboflavin ) FMN (Flavin mononucleotide) Redox reaction • FAD (Flavin adenine dinucleotide) transfer of hydrogens • 3. PP [Nicotinic acid, nicotinamide] NAD+(,Nicotinamide adenine dinucleotide,CoI） Redox reaction • NADP+(Nicotinamide adenine dinucleotide phosphate, CoII) transfer of hydrogens • 4. Pantothentic acid CoASH Coenzyme A, CoA) Transfer of acyl groups • 5. B6 [Pyridoxine, -al,-amine] Pyridoxal, pyridoxamine Transamination, decarboxylation, racemization • 6. Folic acid (FA) FH4(Tetrahydrofolic acid,THFA) Carrier of one-carbon unit • 7. Biotin Coenzyme for carboxylase • 8. C（Ascorbic acid） Redox reaction • 9. Lipoate Transfer of acyl group, Redox reaction • 10. B12（Cobalamine） intramolecular rearrangement, methylation

  6. 2. 1 Vitamin B1 (thiamine) and cocarboxylase(辅羧酶) Sources: husk and bud of grain crops, yeast, some vegetables.  Structure: a thiazole ring + pyrimidine ring to form thiamine.  Thiamine can be transform into thiamine pyrophosphate (TPP) in side body catalyzed by enzyme   Functions: a cocarboxylase catalyzes decarboxylation reaction. The action site is the carbon atom in C2 of thiazole ring.  Vitamin B1 Deficiency: (1) accumulation of pyruvic acid in blood, urea and nervous system. (2) energy Deficiency in nervous system leading to beriberi. (3) inhibition transmission of plant nerve leading to indigestion Thiamine Pyrophosphate

  7. R H +2H N O -2H H O FMN +2H FMNH2 FAD+2H FADH2 2. 2 Vitamin B2 (riboflavin)and lyochrom (yellow coenzyme) Sources: crop seedhusk, vegetables, animal liver and heart. Structure and coenzyme forms: There are two forms of coenzymes derived from vitamin B2: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). ADP B2 FMN FAD

  8. Functions: vitamin B2 is a prosthetic group of yellow enzymes(黄酵素,黄酶）. It playing an important role in oxidation-reduction (Redox) reactions. Vitamin B2 Deficiency Cheilitis （Lip inflammation,唇炎） Glossitis (舌炎 ） Perleche（传染性口角炎 ） Keratitis（角膜炎 ）

  9. 2. 3 Vitamin PP and Coenzyme I and II Sources: meats, grain, peanut vitamin PP can be synthesized inside the body. The raw material for synthesis is tryptophan.  Structure: two forms of this compound― nicotinic acid or niacin and nicotinamide or niacinamide nicotinic acid / niacin nicotinamide / niacinamide

  10. 2e+ H+ 2e+ H+ Coenzyme forms: Oxidation states NAD or NAD+; (coenzyme I or CoI, oxidized) NADP or NADP+(coenzyme II or CoII, oxidized) Reduction state: NADH + H+ (coenzyme I or CoI, reduced) NADPH + H+ (coenzyme II or CoII, reduced) H(NAD),Pi(NADP) Nicotinamide R NAD(P)++2H NAD(P)H+H+ Functions: the coenzyme fordehydrogenases. Some enzymes need NAD, some need NADP, some need either NAD or NADP. Mechanism of dehydrogenation of NAD or NADP: Vitamin PP Deficiency: may result pellagra(糙皮病 ).

  11. 2. 4 Pantothenic acid and CoASources: tissues and organs of plants and animals. Structure: Functions: coenzyme A a carrier of acyl group in metabolism to form acyl-S-CoA. Pantothenic acid Mercaptoacetamide 巯基乙胺 ADP

  12. 2.5. Vitamin B6 and pyridoxal Sources: wide contribution in food, vegetable and fruits―fish, liver, egg yellow, meat, yeast, grains.   Structures:Vitamin B6 includes three interchangeable compounds, pyridoxine.

  13. yridoxal and pyridoxamine and can be phosphated into phosphate state. Pyridoxal phosphate and pyridoxamine phosphate are main forms of coenzymes in metobolism. Functions: the coenzyme playing important roles in amino acid metabolism. (1) transamination: catalyzed by transaminase   (2) Decarbxylation (3) Racemization  Mechanism of catalysis Intermediate―aldimine (Schiff’s base ) Vitamin B6 Deficiency:

  14. R—CH—CO—SCoA - BCCP ADP ATP+CO2 2.6. Biotin Structure: Functions: (1) Fixation of CO2 (2) Carboxylation +

  15. FH4 H 10 5 H 2.7. Folic acid (aka Pteroylglutamic acid (蝶酰谷氨酸即叶酸) Sources: abundant in green leaves Structure: Functional structure: tetrahydrofolic acid (FH4 or THFA) FA Pterin PABA Glu

  16. Function: transport of one-carbon groups in the processes of Glycine to serine Purine ring synthesis Pyrimidine ring synthesis Deficiency:  A typical example of competitive inhibition of enzyme catalytic reaction P-aminobenzoic acid is the component of FH4. Bacteria can synthesize FH4 but human body cannot. When one is infected by bacterium he could take sulfa drug such as sulfanilamide to inhibit the growth of bacteria. Sulfanilamide has similar structure with P-aminobezole acid. Bacteria would take sulfanilamide to synthesize its FH4, but the product is useless. Finally bacteria would be killed because of lack of normal FH4. Because human body is unable to synthesize FH4, there is no effect when taking the drug.

  17. 2.8. Vitamin B12 (cobalamine) Sources:Vitamin B12 can be taken from animal source food―meats, livers, fish and eggs. Structure: a complicate molecule containing cobalt (Co). It is called cobalamine. There are different forms of cobalamine. The variety is depend on the groups( cyanate, water, hydroxyl, etc) combing in cobalt atom.

  18. Functions: (1) coenzyme for mutases (2) coenzyme for metabolism of mono-carbon groups Deficiency:  Lack of vitamin B12 may result some diseases such as pernicious anemia（恶性贫血）. B12 can only be taken by injection in this case.

  19. 2.9 Vitamin C (ascorbic acid) Sources: wide contribution in vegetable and fresh fruits Structure: Structure: Functions: a carrier of hydrogen in oxidation-reduction reactions to maintain the reduction state of cells Deficiency: may result in scurvy. Reduced Vc Oxidized Vc

  20. 2.10. Vitamin A Sources: abundance in fish liver oil and vegetable, especially in carrot. Structure: Function: a key compound in the course of optic vision 11-cis-retinal and 11-cis-vitamin A Deficiency: Lack of vitamin A may result in nyctelopia (night blindness). All-trans-Retinal VA(Retinol) Opsin 11-cis-Retinal Opsin Light Dark Backbone of opsin Photon-sensitive protein----Orhodopsin

  21. 2.11 Vitamin D Sources: Taken from animal source food―livers, milk, eggs etc. Derived from cholesterol. Cholesterol vitamin D2 under the sunlight Structure: vitamin D is derived from cholesterol. Spontaneously Vitamin D3 Previtamin D3 7-dehydrocholesterol Liver Formation of VD3 1, 25-dihydroxy vitamin D3 Kidney 25-hydroxy vitamin D3 Formation of VD2 Ergocalciferol(麦角钙化(甾)醇) 维生素D2 （麦角钙化醇）

  22. Functions: (1) Regulation of calcium and phosphorus metabolism . (2)Maintainance of normal level of calcium and phosphorus in blood. (3)Promotion of normal development of bone. Deficiency: lack of vitamin D may result in the Deficiency of calcium, which turn to suffer from rachitis development inhibition.

  23. tecopherol tecopherol radical 2.12. Vitamin E (Tecopherol,生育酚) Sources: wide distribute in vegetable and fresh fruits, especially plant oils. Structure: there are eight forms of this compound with similar functions. Among them, αtecopherol is the most powerful one. -tecopherol 1--tecopherol

  24. Functions: (1)Essential to animal’s reproduction. (2)Resistant to oxidation so as to protect red blood cells and the activities of some sulfide enzymes. (3)Anti-senescence and anti-tumors. Deficiency:  

  25. 2.13. Vitamin K Sources: animal livers and vegetables Structure: VK1 VK2 VK3 VK4

  26. Functions: the main function of vitamin K is to promote the synthesis of prothrombin (凝血酶原）in liver so as to promote blood coagulation. Deficiency: influent the blood coagulation

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