Co-enzymes

1. PHL – 213 • Biochemistry - I Co-enzymes Enzyme Cofactors and Vitamins • Dr. Vidya.D • Asst. Professor, • College of Pharmacy, • Prince Sattam Bin Abdul Aziz University, • Kingdom of Saudi Arabia

2. Objectives • Definition • Classification • Features • Functions

3. Enzyme --Cofactors • Asimple enzyme is an active enzyme that consists only of protein. • Many enzymes are active only when they combine with cofactors such as metal ions or small molecules. • Acoenzymeis a cofactor that is a small organic molecule such as a vitamin.

4. Enzyme Cofactors (continued)

5. Coenzymes can be classified by their source 1) metabolite coenzymes • synthesized by common metabolites • include nucleoside triphosphates • most abundant is ATP, but also include uridine diphosphate glucose (UDP-glucose) and S-adenosylmethionine • ATP can donate all of its three phosphoryl groups in group-transfer reactions • S-adenosylmethionine can donate its methyl group in biosynthetic reactions. • UDP-glucose is a source of glucose for synthesis of glycogen in animals and starch in plants.

6. 2) vitamin-derived coenzymes • Vitamins are required for coenzyme synthesis and must be supplied in the diet • Lack of particular vitamins causes disease • There are two catagories of vitamins: 1) water-soluble - B vitamins and vit. C • required daily in diet • excess excreted in urine 2) lipid-soluble - vitamins A, D, E, K • Intake must be limited • Stored in fat

7. Function of Coenzymes • A coenzyme prepares the active site for catalytic activity.

8. Metal Ions as Cofactors Many active enzymes require a metal ion. For example, Zn2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond.

9. Some Enzymes and Their Cofactors

10. Salient features of Coenzyme • Coenzymes are heat stable. • They are low-molecular weight substances. • The coenzymes combine loosely with the enzyme molecules and so, the coenzyme can be separated easily by dialysis. • When the reaction is completed, the coenzyme is released from the apo-enzyme, and goes to some other reaction site.

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

12. Descriptions of Water-Soluble Enzymes

13. Thiamin (Vitamin B1) Thiamin • was the first B vitamin identified • is part of the coenzyme thiamin pyrophosphate (TPP) • is used to decarboxylate -keto carboxylic acids • has a recommended daily allowance (RDA) of 1.2 mg; deficiencies include fatigue, poor appetite, weight loss, nerve degeneration, and heart failure

14. Riboflavin (Vitamin B2) Riboflavin • is found in the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) • is needed for good vision and healthy skin • has an RDA of 1.2–1.8 mg; deficiencies include dermatitis, dry skin, tongue inflammation, and cataracts

15. Niacin (Vitamin B3) Niacin • is part of the coenzyme nicotinamide adenine dinucleotide (NAD+) involved in oxidation–reduction reactions • has an RDA of 14–18 mg • deficiency can result in dermatitis, muscle fatigue, and loss of appetite

16. Pantothenic Acid (Vitamin B5) Pantothenic acid • is part of coenzyme A needed for energy production • is involved in glucose and cholesterol synthesis • has an RDA of 5 mg • deficiency can result in fatigue, retarded growth, cramps, and anemia

17. Pyridoxine (Vitamin B6) Pyridoxineand 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 • has an RDA of 1.3–2.0 mg; deficiency may lead to dermatitis, fatigue, and anemia

18. Cobalamin (Vitamin B12) Cobalamin • consists of four pyrrole rings with a Co2+ • is a coenzyme for enzymes that transfer methyl groups and produce red blood cells • has an RDA of 2.0–2.6μg • deficiencies are pernicious anemia, nerve damage, and malformed red blood cells

19. Ascorbic Acid (Vitamin C) Vitamin C • is required in collagen synthesis and healing of wounds • has an RDA of 60–95 mg • deficiencies are scurvy, weakened connective tissue, slow-healing wounds, and anemia

20. Biotin Biotin • is a coenzyme for enzymes that transfer carboxyl groups • has an RDA of 30 g • deficiencies include dermatitis, loss of hair, fatigue, and anemia

21. Folic Acid (Folate) Folic acid (folate) • consists of pyrimidine, p-aminobenzoic acid, and glutamate • forms the coenzyme THF used in the transfer of methyl groups and is involved in the synthesis of nucleic acids • has an RDA of 400  g • deficiencies are abnormal red blood cells, anemia, and poor growth

22. Folic Acid (Folate) (continued)

23. 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

24. Retinol (Vitamin A) Vitamin A • is needed for retinol (vision); synthesis of RNA • has an RDA of 800  g • deficiencies include night blindness, immune system repression, and slowed growth

25. Cholecalciferol (Vitamin D) Vitamin D (D3) • is synthesized in skin exposed to sunlight • regulates the absorption of phosphorus and calcium during bone growth • has an RDA of 5–10 μg • deficiency includes weakened bones

26. Tocopherol (Vitamin E) Vitamin E • is an antioxidant in cells • may prevent the oxidation of unsaturated fatty acids • is found in whole grains and vegetables • has an RDA of 15 mg • deficiencies are hemolysis and anemia

27. 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. • Vitamin K has an RDA of 90–120 μg. • Deficiencies are prolonged bleeding time and bruising

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