229983 lecture 26
- 1. HBC1011 Biochemistry I Lecture 26– Coenzymes and Vitamins Ng Chong Han, PhD ITAR1010, 06-2523751 chng@mmu.edu.my
- 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 FADH2 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+ ?
- 11. Coenzymes: FMN • FMN (Flavin mononucleotide) • Riboflavin-5’-phosphate, is a biomolecule produced from riboflavin (vit B2) 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 (FMNH2) forms occurs in the various oxidoreductases. • FMN is a stronger oxidizing agent than NAD 11
- 12. 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
- 13. 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
- 14. Classification of vitamins 14 Vitamin A Vitamin D Vitamin E Vitamin K
- 15. Water-Soluble Vitamins • Water-soluble vitamins are – soluble in aqueous solutions – cofactors for many enzymes – not stored in the body 15
- 17. Thiamin (Vitamin B1) Thiamin • is part of the coenzyme thiamin pyrophosphate (TPP) • is used to decarboxylate -keto carboxylic acids • deficiencies include fatigue, poor appetite, weight loss, nerve degeneration, and heart failure • Found in cereals, wheat germ, beans, nuts, eggs, yeast and vegetables 17
- 18. Riboflavin (Vitamin B2) 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
- 19. Niacin (Vitamin B3) 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
- 20. Pantothenic Acid (Vitamin B5) 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
- 21. Pyridoxine (Vitamin B6) Pyridoxine and pyridoxal are • two forms of vitamin B6, 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
- 22. Biotin (Vitamin B7) 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
- 23. Folic Acid (Folate)(Vitamin B9) 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
- 24. Cobalamin (Vitamin B12) Cobalamin • consists of four pyrrole rings with a Co2+ • 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 B12 deficiency in the elderly results in less efficient nerve conduction due to poor myelination of peripheral nerves.
- 25. 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 25Vitamin C megadosage
- 26. 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.
- 28. 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.
- 29. Cholecalciferol (Vitamin D) 29 Vitamin D (D3) • 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
- 30. 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
- 31. Menaquinon (Vitamin K) • Vitamin K1 in plants has a saturated side chain. • Vitamin K2 in animals has a long unsaturated side chain. • Vitamin K2 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
- 32. Ubiquinone (Coenzyme Q10) Coenzyme Q10 • Q refers to the quinone chemical group, 10 refers to the number of isoprenyl chemical subunits in its tail • Rich sources of dietary Coenzyme Q10 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
- 33. 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
- 34. 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
- 35. 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 35http://www.phytochemicals.info/
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- 37. 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.
- 38. 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
- 39. supplementation actually appears to be harmful in some disease groups. Antioxidant supplementation and cancer prevention: Randomised trials Experimental Intervention Sample Size Duration Of Study Characteristics Of Participants Study Outcome Bcarotene: 15mg/day Vit E: 30mg/day Selenium: 50mcg/day 29,584 6 years Malnourished Age: 40 69 Lower cancer rate Bcarotene: 20mg/day compared to atocopherol: 50mg/day 29,133 5 8 years Average 6 years Male smokers Age: 50 69 Bcarotene: 20mg/day associated with increase in lung cancer Bcarotene: 30mg/day and retinyl palmitate: 25 000IU/day 18,314 4 years Male and female Age: 45 74 Smoker and/or occupational exposure to asbestos No clear evidence of benefit. Associated with more death Bcarotene: 50mg on alternate days 22,071 11.6 14.2 years, average 12 years Male Age: 40 84 Current/former or nonsmokers No clear evidence of benefit or harm related to cancer risk Bcarotene: 50mg on alternate days 39,876 0.002.72 years, median 2.1 years Female Age: > = 45 No significance difference in incidence of cancer Bcarotene: 25mg/day 864 4 years Adenoma diagnosed Good health No clear evidence of benefit
- 40. Summary 1. Vitamins are often precursors to coenzymes 2. Vitamins are small biomolecules that are needed in small amounts in the diets of higher animals. 3. The water-soluble vitamins are vitamin C (ascorbate, an antioxidant) and the vitamin B complex (components of coenzymes). 4. 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
- 41. Study questions 1. What is a coenzyme? 2. What are the roles of vitamins? 3. What are water soluble vitamins? 4. What are lipid soluble vitamins? 5. What is ubiquinone? 6. What is cytochrome? 41