Transcript fat-soluble vitamins

20.6 Enzyme Cofactors and Vitamins
The ribbon representation
of carboxypeptidase
shows a Zn2+ cofactor
(orange sphere) in the
center of the active site,
held in place by amino
acid residues in the
active site.
Learning Goal Describe the types of cofactors found in enzymes.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
Core Chemistry Skill Describing the Role of Cofactors
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Metal Ions as Cofactors
Many active enzymes
require a metal ion.
For example,
carboxypeptidase requires
a Zn2+ cofactor for the
hydrolysis of the peptide
bond of a C-terminal
aromatic amino acid.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Vitamins and Coenzymes
Vitamins
• are organic molecules that are
essential for normal health and
growth.
• are required in trace amounts.
• need to be obtained from
the diet.
• are grouped into water-soluble
vitamins and fat-soluble
vitamins.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Water-Soluble Vitamins
Water-soluble vitamins must come from our food each
day; they
• are soluble in aqueous solutions and cannot be stored
in the body.
• are cofactors for many enzymes.
• are excreted in urine each day.
• are easily destroyed by heat, oxygen, and ultraviolet
light, so care must be taken in food preparation.
Many of the water-soluble vitamins are precursors of
cofactors required by many enzymes to carry out certain
aspects of catalytic action.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Function of Coenzymes
A coenzyme prepares the active site for catalytic activity.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Thiamine, B1
Thiamine, associated
with coenzyme thiamine
pyrophosphate (TPP),
• is found in the liver,
yeast, whole grain
bread, cereals,
and milk.
• has an RDA of
1.2 mg.
• is necessary to avoid
beriberi, whose
symptoms are fatigue,
poor appetite, and
weight loss.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Riboflavin, B2
Riboflavin, associated with
coenzymes flavin adenine
dinucleotide (FAD) and flavin
mononucleotide (FMN),
• is found in the liver, beef,
chicken, eggs, green
leafy vegetables, dairy
foods, peanuts, and
whole grains.
• has an RDA of
1.2–1.8 mg.
• is necessary to avoid
dermatitis; dry skin; red,
sore tongue; and
cataracts.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Niacin, B3
Niacin, associated with
coenzymes nicotinamide
adenine dinucleotide (NAD2+)
and nicotinamide adenine
dinucleotide phosphate
(NADP2+),
• is found in brewer’s yeast,
chicken, beef, fish, liver,
brown rice, and whole
grains.
• has an RDA of
14–18 mg.
• is necessary to avoid
pellagra: dermatitis,
muscle fatigue, loss of
appetite, diarrhea, and
mouth sores.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Pantothenic Acid, B5
Pantothenic acid,
associated with
coenzyme A,
• is found in salmon,
beef, liver, eggs,
brewer’s yeast,
whole grains, and
fresh vegetables.
• has an RDA of 5 mg.
• is necessary to avoid
fatigue, retarded
growth, muscle
cramps, and anemia.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Pyridoxine, B6
Pyridoxine, associated
with pyridoxal
phosphate (PLP),
• is found in meat,
liver, fish, nuts,
whole grains, and
spinach.
• has an RDA of
1.3–2.0 mg.
• is necessary to avoid
dermatitis, fatigue,
anemia, and
retarded growth.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Folic Acid, B9
Folic acid, associated with
tetrahydrofolate (THF),
• is found in green leafy
vegetables, beans,
meat, seafood, yeast,
asparagus, and whole
grains enriched with
folic acid.
• has an RDA of 400 mcg.
• is necessary to avoid
abnormal red blood
cells, anemia, intestinal
tract disturbances, loss
of hair, growth
impairment, and
depression.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Cobalamin, B12
Cobalamin, associated
with methylcobalamin,
• is found in liver, beef,
kidney, chicken, fish,
and milk products.
• has an RDA of
2.0–2.6 mcg.
• is necessary to avoid
pernicious anemia,
malformed red blood
cells, and nerve
damage.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Ascorbic Acid, C
Ascorbic acid
• is found in blueberries,
citrus fruits,
strawberries,
cantaloupe, tomatoes,
peppers, broccoli,
cabbage, and spinach.
• has an RDA of
75–90 mg.
• is necessary to avoid
scurvy: bleeding gums,
weakened connective
tissues, slow-healing
wounds, and anemia.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Biotin, H
Biotin, associated
with biocytin,
• is found in liver,
yeast, nuts,
and eggs.
• has an RDA of
30 mcg.
• is necessary to
avoid dermatitis,
loss of hair, fatigue,
anemia, and
depression.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Identify each enzyme as
1) a simple enzyme.
2) an enzyme that requires 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
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Identify each enzyme as
1) a simple enzyme.
2) an enzyme that requires a cofactor.
2 A. requires Mg2+ for hydrolysis of phosphate
esters
2 B. requires vitamin B3 to transfer an acetyl group
1 C. is active with four polypeptide subunits
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Fat-Soluble Vitamins
Fat-soluble vitamins
• include A, D, E, and K and are not involved as
coenzymes in catalytic reactions.
• are soluble in lipids but not in aqueous solutions.
• are stored in the body and not eliminated in urine.
• are important in vision, bone formation,
antioxidants, and blood clotting.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Retinol (Vitamin A)
Vitamin A, an antioxidant,
• is needed for retinol (vision) and synthesis of RNA.
• has an RDA of 800 g.
• is necessary to avoid night blindness, immune system
repression, and slowed growth.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
• is necessary to avoid weakened bones.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Tocopherol (Vitamin E)
Vitamin E
• is an antioxidant in cells.
• is found in whole grains and vegetables.
• has an RDA of 15 mg.
• is necessary to avoid hemolysis and anemia.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Menaquinon (Vitamin K)
Vitamin K
• is needed for the synthesis of zymogens for blood clotting.
• has an RDA of 90–120 mcg.
• is necessary to avoid prolonged bleeding time and bruising.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Identify each of the following as a water-soluble
vitamin (WS) or fat-soluble vitamin (FS):
A. folic acid
B. retinol (vitamin A)
C. vitamin C
D. vitamin E
E. niacin
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Identify each of the following as a water-soluble
vitamin (WS) or fat-soluble vitamin (FS):
A. folic acid
WS
B. retinol (vitamin A)
FS
C. vitamin C
WS
D. vitamin E
FS
E. niacin
WS
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Identify the vitamin associated with each of the following:
1) riboflavin (B2)
2) vitamin A
3) vitamin K
4) vitamin D
5) ascorbic acid
A.
B.
C.
D.
E.
collagen formation
part of the coenzymes FAD and FMN
absorption of phosphorus and calcium in bone
vision
blood clotting
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Identify the vitamin associated with each of the following:
1) riboflavin (B2)
2) vitamin A
3) vitamin K
4) vitamin D
5) ascorbic acid
5
1
4
2
3
A.
B.
C.
D.
E.
collagen formation
part of the coenzymes FAD and FMN
absorption of phosphorus and calcium in bone
vision
blood clotting
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Concept Map
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.