1 Chapter 20 Enzymes and Vitamins 20.6 Enzyme Cofactors and Vitamins Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 Enzyme Cofactors  A simple 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.  A coenzyme is a cofactor that is a small organic molecule such as a vitamin.

3 Enzyme Cofactors Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

4 Function of Coenzymes A coenzyme prepares the active site for catalytic activity. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

5 Metal Ions as Cofactors Many active enzymes require a metal ion. Zn 2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

6 Some Enzymes and Their Cofactors TABLE 20.8 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

7 Learning Check Identify each enzyme as 1) A simple enzyme 2) An enzyme that required a cofactor A. Requires Mg 2+ for hydrolysis of phosphate esters. B. Requires vitamin B 3 to transfer an acetyl group. C. Is active with four polypeptide subunits.

8 Solution Identify each enzyme as 1) A simple enzyme 2) An enzyme that required a cofactor A. 2 Requires Mg 2+ for hydrolysis of phosphate esters. B. 2 Requires vitamin B 3 to transfer an acetyl group. C. 1 Is active with four polypeptide subunits.

9 Water-Soluble Vitamins Water-soluble vitamins are  Soluble in aqueous solutions.  Cofactors for many enzymes.  Not stored in the body. TABLE 20.9 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

10 Fat-Soluble Vitamins Fat-soluble vitamins are  Vitamins A, D, E, and K.  Soluble in lipids, but not in aqueous solutions.  Important in vision, bone formation, antioxidants, and blood clotting.  Stored in the body. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

11 Learning Check Identify each compound as a water-soluble vitamin (W) fat-soluble vitamin(F) 1. Folic acid 2. Retinol (Vitamin A) 3. Vitamin C 4. Vitamin E 5. Niacin

12 Solution Identify each compound as a: water-soluble vitamin (W) fat-soluble vitamin(F) 1. W Folic acid 2. F Retinol (Vitamin A) 3. W Vitamin C 4. F Vitamin E 5. W Niacin

13 Thiamin (Vitamin B 1 ) Thiamin  Was the first B vitamin identified.  Is part of the coenzyme thiamin pyrophosphate (TPP).  Is used to decarboxylate  -keto carboxylic acids.  RDA is 2 mg; deficiencies include fatigue, poor appetite, weight loss, nerve degeneration, heart failure  Sources are liver, yeast, whole grains, cereals, and milk.

14 Riboflavin (Vitamin B 2 ) Riboflavin  Is found in the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN).  Is needed for good vision and healthy skin.  RDA is 1.7 mg, deficiencies include dermatitis, dry skin, tongue inflammation, cataracts  Sources are liver, chicken, eggs, green leafy vegetables, dairy foods, peanuts, and whole grains. ribitol flavin

15 Niacin (Vitamin B 3 ) Niacin  Is part of the coenzyme nicotinamide adenine dinucleotide (NAD + ) involved in oxidation-reduction reactions.  RDA is mg.  Deficiency can result in dermatitis, muscle fatigue, and loss of appetite.  Sources are brewer’s yeast, chicken, beef, fish, liver, brown rice, and whole grains.

16 Pantothenic Acid (Vitamin B 5 ) Pantothenic acid  Is part of coenzyme A needed for energy production as well as glucose and cholesterol synthesis.  RDA is 10 mg; deficiency can result in fatigue, retarded growth, cramps, and anemia.  Is found in salmon, meat, eggs, whole grains, and vegetables.

17 Pyridoxine (Vitamin B 6 ) Pyridoxine and pyridoxal are  Two forms of vitamin B 6, which are converted to the coenzyme pyridoxal phosphate (PLP).  PLP is required in the transamination of amino acids and decarboxylation of carboxylic acids.  RDA is 1 mg; deficiency may lead to dermatitis, fatigue, and anemia.  Sources are meat, liver, fish, nuts, whole grains, spinach.

18 Cobalamin (Vitamin B 12 ) Cobalamin  Consists of four pyrrole rings with a Co 2+.  Is a coenzyme for enzymes that transfer methyl groups and produce red blood cells.  RDA is3 μg; deficiencies are pernicious anemia, nerve damage, and malformed red blood cells.  Sources are liver, beef, kidney, chicken, fish, milk products.

19 Ascorbic Acid (Vitamin C) Vitamin C  Is required in collagen synthesis, healing of wounds.  RDA is 60 mg; deficiencies are scurvy, weakened connective tissue, slow- healing wounds, and anemia.  Sources include: blueberries, citrus fruits, tomatoes, peppers, broccoli, red and green vegetables. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

20 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 the synthesis of nucleic acids.  RDA is 0.4 mg; deficiencies are abnormal red blood cells, anemia, and poor growth.  Sources are green leafy vegetables, beans, meat, seafood, yeast, asparagus, and whole grains enriched with folic acid.

21 Folic Acid (Folate) Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

22 Vitamin A  Is needed for retinol (vision); synthesis of RNA.  RDA is 3 mg; deficiencies include night blindness, immune system repression, and slowed growth.  Sources are meats and beta-carotenes in plants, yellow and green fruits and vegetables. retinol beta-carotene

23 Vitamin D Vitamin D (D 3 )  Is synthesized in skin exposed to sunlight.  Regulates the absorption of phosphorus and calcium during bone growth.  RDA is 10 μg; deficiencies are weakened bones.  Sources are sunlight, cod liver oil, eggs, and enriched milk.

24 Vitamin E  Is an antioxidant in cells.  May prevent the oxidation of unsaturated fatty acids.  Is found in whole grains, and vegetables.  RDA is 10 mg; deficiencies are hemolysis and anemia.  Sources are meats, whole grains, vegetables, and vegetable oils.

25 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.  RDA is 80 μg; deficiencies are prolonged bleeding time, and bruising.  Sources are liver, spinach, and cauliflower. 3 n Vitamin K 1 (phylloquinone)Vitamin K 2 (menaquinone)

26 Learning Check Identify the vitamin associated with each 1) Thiamin (B 1 )2) Vitamin A 3) Vitamin K4) Vitamin D 5) Ascorbic Acid A. Collagen formation B. Beriberi C. Absorption of phosphorus and calcium in bone D. Vision E. Blood clotting

27 Solution Identify the vitamin associated with each 1) Thiamin (B 1 )2) Vitamin A 3) Vitamin K4) Vitamin D 5) Ascorbic Acid A. 5 Collagen formation B. 1 Beriberi C. 4 Absorption of phosphorus and calcium in bone D. 2 Vision E. 3 Blood clotting