229983 lecture 26

biochemistry

1. HBC1011 Biochemistry I Lecture 26– Coenzymes and Vitamins Ng Chong Han, PhD ITAR1010, 06-2523751 [email protected]

2. Overview Coenzymes classification ATP, NAD + /NADH, NADP + /NADPH, FAD, FMN Classification of vitamins Water soluble vitamins Fat soluble vitamins Ubiquinone Cytochromes 2

3. Coenzyme classification 3 Holoenzymes : Active forms of enzymes. Apoenzyme : Enzymes that require a cofactor but are not bound by one. Cofactor : Non-protein chemical compound (coenzyme) or metallic ion that is required for a protein's biological activity. 

4. Coenzymes Coenzymes, is a cofactor that consists of small organic molecules, many of which are derived from vitamins A coenzyme prepares the active site for catalytic activity. 4 Coenzymes are small organic molecules that can be loosely or tightly bound to an enzyme. Coenzymes transport chemical groups from one enzyme to another.

5. Coenzymes: ATP Adenoside triphosphate (ATP) Often called as “molecular unit of currency” Energy used by all cells The structure of this molecule consists of a purine base ( adenine ) , attached to the 1' carbon atom of a pentose sugar (ribose), three phosphate groups are attached at the 5' carbon atom of the pentose sugar Energy is released when breaking the high-energy bonds between the last two phosphates in ATP Hydrolysis by enzyme, ATPase 5

6. Coenzymes: NAD + /NADH NAD (nicotinamide adenine dinucleotide) Consists of two nucleotides joined through their phosphate groups, nicotinamide (reactive part) and adenine base Exists in two forms: oxidized form, NAD + ; reduced form, NADH (when it picks up two electrons and one hydrogen ion) Coenzyme found in all living cells A major electron carrier in the oxidation of fuel molecules. 6

7. Coenzymes: NADP + /NADPH NADPH (nicotinamide adenine dinucleotide phosphate) NAD + is usually associated with catabolic reactions and NADP + is usually associated with anabolic reactions (lipid and nucleic acid synthesis) NADPH acts as a reducing agent, is the reduced form of NADP + 7

8. NAD + /NADH vs NADP + /NADPH ratio NAD + /NADH ratio The balance between the oxidized and reduced forms of nicotinamide adenine dinucleotide This ratio is an important for the redox state of a cell, a measurement that reflects both the metabolic activities and the health of cells.  controlling the activity of several key enzymes, including glyceraldehyde 3-phosphate dehydrogenase and pyruvate dehydrogenase. In healthy mammalian tissues, estimates of the ratio between free NAD + and NADH in the cytoplasm typically lie around 700; the ratio is thus favorable for oxidative reactions.  In contrast, the NADP + /NADPH ratio is normally about 0.005, so NADPH is the dominant form of this coenzyme .  These different ratios are key to the different metabolic roles of NADH and NADPH. 8

9. Coenzymes: FAD FAD (Flavin adenine dinucleotide) is another major electron carrier in the oxidation of fuel molecules other than NAD FAD + is reduced to FADH 2 upon bonding to two hydrogen atoms, become energy-carrying molecule 9 The reactive part of FAD is its isoalloxazine , derivative of vitamin riboflavin What is the common feature to ATP, FAD, NAD + ?

10. Coenzymes: FMN FMN (Flavin mononucleotide) Riboflavin-5’-phosphate , is a biomolecule produced from riboflavin ( vit B 2 ) by the enzyme riboflavin kinase Functions as prosthetic group of various oxidoreductases including NADH dehydrogenase During the catalytic cycle, a reversible interconversion of the oxidized (FMN), semiquinone (FMNH • ) and reduced (FMNH 2 ) forms occurs in the various oxidoreductases. FMN is a stronger oxidizing agent than NAD 11

11. What are vitamins? Organic nutrients required in small quantities for a variety of biochemical functions Nutrients that our body does not make on its own. Obtain from the foods we eat, or via vitamin supplements Essential for providing good health and are necessary for many life functions. The most prominent function is as cofactors for enzymatic reactions 12 VS

12. Role of vitamins Essential for growth, development, metabolism and general health of the body If not supplied in adequate quantities by the diet, they result in a number of deficiencies Needed by body to make enzymes and hormones Do not contain any calories and do not impart energy directly, but are needed by the body to convert food into energy 13

13. Classification of vitamins 14 Vitamin A Vitamin D Vitamin E Vitamin K

14. Water-Soluble Vitamins Water-soluble vitamins are soluble in aqueous solutions cofactors for many enzymes not stored in the body 15

15. Water-Soluble vitamins 16

16. Thiamin (Vitamin B 1 ) Thiamin is part of the coenzyme thiamin pyrophosphate (TPP) is used to decarboxylate -keto carboxylic acids d eficiencies include f atigue, poor appetite, weight loss, nerve degeneration, and heart failure Found in cereals, wheat germ, beans, nuts, eggs, yeast and vegetables 17

17. Riboflavin (Vitamin B 2 ) Riboflavin is found in the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) Involved in redox reactions of C-C bonds is needed for good vision and healthy skin deficiencies include dermatitis, dry skin, tongue inflammation, and cataracts Found in liver, kidney, dairy products, eggs, yeast, meat, and vegetables 18

18. Niacin (Vitamin B 3 ) Niacin is part of the coenzyme nicotinamide adenine dinucleotide (NAD + ) involved in oxidation – reduction reactions deficiency can result in dermatitis, muscle fatigue, and loss of appetite Found in meats, fish, yeast, eggs, dairy, grains, nuts, legumes, roasted coffee 19

19. Pantothenic Acid (Vitamin B 5 ) Pantothenic acid is part of coenzyme A needed for energy production is involved in glucose and cholesterol synthesis deficiency can result in fatigue, retarded growth, cramps, and anemia Found in yeast, liver, and cereals 20

20. Pyridoxine (Vitamin B 6 ) Pyridoxine and pyridoxal are two forms of vitamin B 6 , which are converted to the coenzyme pyridoxal phosphate (PLP) required in the transamination of amino acids and decarboxylation of carboxylic acids deficiency may lead to dermatitis, fatigue, and anemia Found in meat, salmon, nuts, potatoes, bananas, and cereals 21

21. Biotin (Vitamin B 7 ) 22 Biotin formerly known as  vitamin H  or  coenzyme R is a coenzyme for enzymes that transfer carboxyl groups Aids in cell growth and fatty acid production deficiencies include dermatitis, loss of hair, fatigue, and anemia Found in egg yolk, liver, and some vegetables

22. Folic Acid (Folate)(Vitamin B 9 ) 23 Folic acid (folate) consists of pyrimidine, p - aminobenzoic acid, and glutamate forms the coenzyme tetrahydrofolate, THF used in the transfer of methyl groups and is involved in the synthesis of nucleic acids deficiencies are abnormal red blood cells, anemia, and poor growth Found in green veggies, yeast, liver, legumes, whole grains, some fruits

23. Cobalamin (Vitamin B 12 ) Cobalamin consists of four pyrrole rings with a Co 2+ coenzyme for enzymes that transfer methyl groups and produce red blood cells deficiencies are pernicious anemia, nerve damage, and malformed red blood cells Found in meat, shellfish, liver, dairy products and eggs 24 Vitamin B 12 deficiency in the elderly results in less efficient nerve conduction due to poor myelination of peripheral nerves.

24. Ascorbic Acid (Vitamin C) Vitamin C is required in collagen synthesis and healing of wounds deficiencies are scurvy, weakened connective tissue, slow-healing wounds, and anemia Found in citrus fruits, cruciferous veggies, tomatoes, dark green leafy, berries, mangos, melons 25 Vitamin C megadosage

25. Fat-Soluble Vitamins Fat-soluble vitamins are vitamins A, D, E, and K soluble in lipids but not in aqueous solutions stored in the body important in vision, bone formation, antioxidants, and blood clotting 26 Toxicity: Lipid-soluble vitamins may accumulate in the fatty tissue, leading to toxic effect.

26. Fat-soluble vitamins 27

27. Retinol (Vitamin A) 28 Vitamin A is needed for retinol (vision); synthesis of RNA deficiencies include night blindness, immune system repression, and slowed growth Many retinoid forms of vitamin A, such as retinoic acid, adapalene may be used in the treatment of acne, inflammatory skin disorders. 

28. Cholecalciferol (Vitamin D) 29 Vitamin D (D 3 ) is synthesized in skin exposed to sunlight regulates the absorption of phosphorus and calcium during bone growth deficiency includes weakened bones Found in salmon, tuna, eggs, fortified milk, juices, beef liver

29. Tocopherol (Vitamin E) Vitamin E Vitamin E family: tocopherols (saturated) and  tocotrienols (unsaturated) antioxidant, may prevent the oxidation of unsaturated fatty acids deficiencies: hemolysis and anemia, male infertility Found in wheat germ, nuts, seeds, green leafy vegetables, kiwi, mango, tomatoes 30

30. Menaquinon (Vitamin K) Vitamin K 1 in plants has a saturated side chain. Vitamin K 2 in animals has a long unsaturated side chain. Vitamin K 2 is needed for the synthesis of zymogens for blood clotting and healthy bone growth. Deficiencies are prolonged bleeding time and bruising Found in green leafy vegetables, soybean oil, olive oil, canola oil 31

31. Ubiquinone (Coenzyme Q 10 ) Coenzyme Q 10 Q refers to the quinone chemical group, 10 refers to the number of isoprenyl chemical subunits in its tail Rich sources of dietary Coenzyme Q 10 include mainly meat, poultry, fish, soybean, canola oils and nuts Functions Participates in aerobic cellular respiration, generating energy as ATP lipid-soluble antioxidant to prevent lipid peroxidation 32

32. Cytochromes Cytochromes are hemeproteins containing heme groups and are primarily responsible for the generation of ATP via electron transport. They are capable of performing oxidation and reduction They are found either as monomeric proteins (e.g., cytochrome c) or as subunits of bigger enzymatic complexes that catalyze redox reactions. 33

33. Cytochromes P450 Proteins of the superfamily containing  heme  as a cofactor The term P450 is derived from the spectrophotometric peak at the wavelength 450 nm when the enzyme is in the reduced state. Located either in the inner membrane of mitochondria or in the endoplasmic reticulum of cells.  Functions:  hormone synthesis and breakdown, cholesterol synthesis, vitamin D metabolism and drug detoxification (75% of drug) 34

34. Phytochemicals Chemicals with biological activity produced by plants through primary or secondary metabolism. Play a role in plant growth or defense against competitors, pathogens, or predators. They are non-essential nutrients, meaning that they are not required by the human body for sustaining life. Plant produce these chemicals to protect themselves but they can also protect humans against diseases. Example: lycopene (tomatoes), isoflavones (soy), allicin (garlic), carotenoids (fruits, carrots), flavonoids (fruits, vegetables), polyphenols (tea, grapes). Functions: Antioxidants, hormonal action, anti-bacterial effect 35 http:// www.phytochemicals.info /

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36. Why most vitamin supplements give you expensive urine? The biggest deficiency in the Western diet comes from a lack of fruits and vegetables and a lack of Omega 3 fatty acids.  Prof. Rory Collins from the University of Oxford studied vitamin consumption in 20,000 people over 5 years and concluded that, "Vitamin pills are a waste of time. The Harvard physicians study group on 22,071 male physicians found that taking isolated supplements of beta-carotene was shown to be of no benefit.  37 Vitamin pills are not fruits and vegetables!!! While vitamin supplements can help those with specific deficiencies, a good diet is enough to keep the average person healthy.

37. Antioxidants: Pro- or Anti-Cancer? Fruits and vegetables contain essential vitamins, minerals, fibre and other nutrients including antioxidants. A good start to optimal health is to eat at least 5 servings of fruits and vegetables a day.  Individuals who have diets rich in fruits and vegetables may have a reduced risk of cancer compared with those who eat a much higher proportion of high-fat and processed foods. Numerous studies have examined the association between dietary antioxidant intake and the risk of cancer.   As shown,  a major surprise of these studies has been that antioxidant supplementation actually appears to be harmful in some disease groups . Should I take antioxidants? If you're being treated for cancer, it is not a good idea to take high doses of antioxidant nutrients as they may interfere with cancer treatment. 38

38. Summary Vitamins are often precursors to coenzymes Vitamins are small biomolecules that are needed in small amounts in the diets of higher animals. The water-soluble vitamins are vitamin C (ascorbate, an antioxidant) and the vitamin B complex (components of coenzymes). The fat-soluble vitamins are vitamin A (a precursor of retinol), D (a regulator of calcium and phosphorus metabolism), E (an antioxidant in membranes), and K (a participant in the carboxylation of glutamate). 40

39. Study questions What is a coenzyme? What are the roles of vitamins? What are water soluble vitamins? What are lipid soluble vitamins? What is ubiquinone? What is cytochrome? 41