1 Chapter 20 Enzymes and Vitamins 20.6 Enzyme Cofactors and Vitamins Copyright © 2007 by Pearson...

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.

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Enzyme Cofactors


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Function of Coenzymes

• A coenzyme prepares the active site for catalytic activity.


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Metal Ions as Cofactors

Many active enzymesrequire a metal ion.

Zn2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond.


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Some Enzymes and Their Cofactors

TABLE 20.8


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Learning Check

Identify each enzyme as

1) A simple enzyme

2) An enzyme that required a cofactor

A. Requires Mg2+ for hydrolysis of phosphate esters.

B. Requires vitamin B3 to transfer an acetyl group.

C. Is active with four polypeptide subunits.

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Solution

Identify each enzyme as

1) A simple enzyme

2) An enzyme that required a cofactor

A. 2 Requires Mg2+ for hydrolysis of phosphate esters.

B. 2 Requires vitamin B3 to transfer an acetyl group.

C. 1 Is active with four polypeptide subunits.

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Water-Soluble Vitamins

Water-soluble vitamins are Soluble in aqueous solutions. Cofactors for many enzymes. Not stored in the body.

TABLE 20.9


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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.


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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

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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

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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. RDA is 2 mg; deficiencies include fatigue, poor appetite,

weight loss, nerve degeneration, heart failure Sources are liver, yeast, whole grains, cereals, and milk.

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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. 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.O

O

OH OH OH

OHCH2CHCHCHCH2

H3C

H3C HN

NN

N

ribitol

flavin

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Niacin (Vitamin B3)

Niacin Is part of the coenzyme

nicotinamide adenine dinucleotide (NAD+) involved in oxidation-reduction reactions.

RDA is 13-18 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.

OH

O

C

N

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Pantothenic Acid (Vitamin B5)

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.

CH3

CH3 OOH

H

O

OHCCH2CH2NCCHCCH2HO

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Pyridoxine (Vitamin B6)

Pyridoxine and pyridoxal are Two forms of vitamin B6, 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.

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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.

RDA is3 μg; deficiencies are pernicious anemia, nerve damage, and malformed red blood cells.

Sources are liver, beef, kidney, chicken, fish, milk products.

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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.

O

HO OH

CH2OH

CHOHO


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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.

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Folic Acid (Folate)


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Vitamin A

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.

CH3

CH3H3CCH2OH

CH3CH3

H3C

CH3H3CCH3CH3

CH3CH3

CH3

CH3H3C

retinol

beta-carotene

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Vitamin D

Vitamin D (D3) 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.

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Vitamin E

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.

CH3CH3CH3

CH3

CH3

CH3

H3C

HO

CH3

O

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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.

RDA is 80 μg; deficiencies are prolonged bleeding time, and bruising.

Sources are liver, spinach, and cauliflower.

CH3CH3O

O

CH3

CH3

3 n

Vitamin K1 (phylloquinone) Vitamin K2 (menaquinone)CH3CH3O

O

CH3

CH3

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Learning Check

Identify the vitamin associated with each1) Thiamin (B1) 2) Vitamin A

3) Vitamin K 4) Vitamin D5) Ascorbic Acid

A. Collagen formationB. BeriberiC. Absorption of phosphorus and calcium in bone D. VisionE. Blood clotting

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Solution

Identify the vitamin associated with each

1) Thiamin (B1) 2) Vitamin A

3) Vitamin K 4) 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

1 Chapter 20 Enzymes and Vitamins 20.6 Enzyme Cofactors and Vitamins Copyright © 2007 by Pearson...

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Transcript of 1 Chapter 20 Enzymes and Vitamins 20.6 Enzyme Cofactors and Vitamins Copyright © 2007 by Pearson...