Transcript Amino Acids, Proteins, and Enzymes

Chapter 20 Enzymes and Vitamins
20.6
Enzyme Cofactors and Vitamins
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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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
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Function of Coenzymes
• A coenzyme prepares the active site for catalytic
activity.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Metal Ions as Cofactors
Many active enzymes
require a metal ion.
Zn2+, 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
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Some Enzymes and Their
Cofactors
TABLE 20.8
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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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
H3C
N
H3C
N
N
flavin
N
H
O
CH2 CH CH CH CH2 OH
OH OH OH
ribitol
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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.
O
C
OH
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 OH O
HO CH2 C
CH3
O
CH C N CH2
CH2 C OH
H
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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, slowhealing wounds, and anemia.
 Sources include: blueberries,
citrus fruits, tomatoes,
peppers, broccoli, red and
green vegetables.
O
HO
O
CH2OH
CHOH
OH
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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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)
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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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.
H3C
CH3
CH3
H3C
CH3
CH3
CH3
H3C
CH3
CH3
CH3
CH3
H3C
CH3
beta-carotene
CH3
CH2OH
retinol
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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.
CH3
HO
CH3
H3C
O
CH3
CH3
CH3
CH3
CH3
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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.
O
O
CH3
CH3
CH3
O
CH3
Vitamin K1 (phylloquinone)
3
CH3
CH3
O
CH3
Vitamin K2 (menaquinone)
n
CH325
Learning Check
Identify the vitamin associated with each
1) Thiamin (B1)
2) Vitamin A
3) Vitamin K
4) Vitamin D
5) Ascorbic Acid
A.
B.
C.
D.
E.
Collagen formation
Beriberi
Absorption of phosphorus and calcium in bone
Vision
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.
B.
C.
D.
E.
5
1
4
2
3
Collagen formation
Beriberi
Absorption of phosphorus and calcium in bone
Vision
Blood clotting
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