Vitamins

1. Enzymes and Vitamins
M. Faisal Shahid and
Humaira Faraz (Ph.D.)
PCMD, ICCBS, University
of Karachi.

2. • Proteins that act as biological
catalysts.
• Each cell in the human body contains
thousands of different enzymes.
• Highly specific to substrate.
• Works by lowering the activation energy,
changing the reaction pathway that
provides a lower energy route.
• As catalysts enzymes are not consumed in
the reactions
• A few enzymes are now known to be
ribonucleic acids (RNA)-Ribozymes
Enzymes
Figure 1: Schematic diagram of
enzyme activity mechanism.

3. Simple and Conjugated Enzymes
• Usually globular proteins
• SOME are conjugated proteins
• Simple enzyme: Composed only of protein
(amino acid chains)
• Conjugated enzyme: has a non-protein part in
addition to a protein part.
1. Apoenzyme: Protein part; inactive alone
2. Co-factor: Non-protein part:
If organic: Termed coenzyme /co-
substrate.
If inorganic: Moiety/ Activator
• Apoenzyme + cofactor = Holoenzyme Figure 2: Enzyme Anatomy

4. Classification of Enzymes
• According to function:
– Type of reaction catalyzed
– Identity of the substrate
• A substrate is the reactant in an enzyme-catalyzed
reaction:
– the substrate is the substance upon which the
enzyme “acts.”
– e. g., In the fermentation process, sugar is converted
to alcohol, therefore in this reaction sugar is the
substrate

5. Enzyme Naming Process (Nomenclature)
1. Suffix:
– Active form types: urease, sucrase, and lipase
– Exceptions The suffix -in is used e.g., trypsin,
chymotrypsin, and pepsin
2. Reaction catalyzed Suffix:
– e.g., Oxidase - catalyzes an oxidation reaction
– e.g., Hydrolase - catalyzes a hydrolysis reaction
3. According to type of reaction
– e.g. glucose oxidase, pyruvate carboxylase, and succinate
dehydrogenase

6. Enzyme Classification
Enzymes are grouped into six major classes based on the types of
reactions they catalyze
Class Reaction Catalyzed
1. Oxidoreductases Oxidation-reductions
2. Transferases Functional group transfer reactions
3. Hydrolases Hydrolysis reactions
4. Lyases Reactions involving addition of a group to a double bond
or removal of groups to form double bonds
5. Isomerase Isomerization reactions
6. Ligases
Reactions involving bond formation coupled with ATP
hydrolysis
Table 1. Enzyme Classes

7. Coenzymes / Cofactors
• Water-soluble vitamins, which include all B-vitamins and Vitamin C, act as
coenzymes or coenzyme precursors
• cofactors are bound to the enzyme for it to maintain the correct
configuration at the active site
• provide additional chemically reactive functional group
Figure 3: Enzyme Anatomy

8. Enzyme Structure
Coenzymes / Cofactors
Figure 4: Enzyme Anatomy

9. Enzyme Structure
Coenzymes / Cofactors
Inorganic Cofactors
Metal Ion Enzymes
; Fe3+
Ca 2+
Cu2+
Fe2+
Mg2+
Mn2+
K+
Zn2+
Thromboplastin
Tyrosinase, cytochrome oxidase
Cytochrome oxidase, catalase, dehydrogenase
Pyruvate kinase
Arginase, pyruvate carboxylase, phosphatase, succinic dehydrogenase,
glycosyl transferases, cholinesterase
Pyruvate kinase
Carbonic anhydrase, carboxypeptidase, lactic dehydrogenase, alcohol
dehydrogenase

10. Vitamins (General Characteristics)
• Vitamin: Organic compound essential for proper functioning of the body
• Essential Requirement (Cant be synthesized by body)
• Micro-nutrient but essential thus termed “Vital”.
– 1 gram of vitamin B is sufficient for 500,000 people
• Can be obtained from balanced diet
• Supplemental vitamins may be needed after illness
• Acts as “CO-ENZYMES”
• Water-Soluble (B and C) and Fat-Soluble (A, D, E and K)

11. General Characteristics of Vitamins
Table 2: Enzyme Classification

12. Section 21.12
General Characteristics of Vitamins
Table 3: Vitamin functions

13. Section 21.12
General Characteristics of Vitamins
Vitamin C (Ascorbic acid)
• Essential Nutrient
• Co-substrate in the formation of structural protein collagen
- Hydroxylation of lysine and proline in collagen formation are
catalyzed by enzymes that require ascorbic acid (Vit. C) and
iron.
- Vit. C deficiency symptoms include:
Skin lesions
Fragile blood vessels
Loose teeth and Bleeding gums
• Also Involved in metabolism of certain amino acids

14. The Vitamin B
• Major function: Components of many coenzymes
• Temporary carriers of atoms or functional groups in redox and group transfer reactions
associated with metabolism.
• The preferred and alternative names for the B vitamins
– Thiamin (vitamin B1)
– Riboflavin (vitamin B2)
– Niacin (nicotinic acid, nicotinamide, vitamin B3)
– Pantothenic acid (vitamin B5)
– Vitamin B6 (pyridoxine, pyridoxal, pyridoxamine)
– Folate (folic acid)
– Vitamin B12 (cobalamin)
– Biotin

15. The B Vitamins
Table 4: The Vitamin B Complex

16. Fat-Soluble Vitamins
Vitamins A, D, E, K
• Involved in plasma membrane processes
• Possess with fewer functional groups
• Occur in the lipid fractions of their sources
• Have double bonds or phenol rings, so oxidizing agents readily
attack them
• Destroyed by prolonged exposures to air or to the organic
peroxides.
• Acts as anti-oxidants

17. Fat-Soluble Vitamins
Vitamin A
• C20H30O (Primary Alcohol)
• Sources: Cod-liver oil and
other fish-liver oils, animal
liver and dairy products.
• Provitamin A found in the form
of carotenes. Provitamins have
NO vitamin activity.
• After ingestion in the diet, -
carotene is cleaved at the give
2 molecules of Vit.A. Figure 5: Vitamin A structure

18. Fat-Soluble Vitamins
Functions of Vitamin A
• Vision: In eye, Vitamin A combines with “Opsin" protein to form
the visual pigment Rhodhopsin. It converts light energy into nerve
impulses that are sent to the brain.
• Regulating Cell Differentiation of bone marrow cells white blood
cells and red blood cells.
• Maintenance of the health of epithelial tissues via epithelial tissue
differentiation.
– lack of vitamin A causes skin surface to become drier and
harder than normal.
• Reproduction and Growth: Participates in sperm and fetal
development.

19. Fat-Soluble Vitamins
Vitamin D - Sunshine Vitamin
• The antirachitic vitamin
• Necessary for the normal
calcification of bone tissue
• It controls correct ratio of Ca and
P for bone mineralization
(hardening)
• Two forms active in the body:
Vitamin D2 and D3
• Pigment in the skin, 7-
dehydrocholesterol, is a
provitamin D; when irradiated by
the sun becomes converted to
Vit. D3
• humans exposed to sunlight year-
round do not require dietary Vit. D
Figure 6: Vitamin D structure

20. Fat-Soluble Vitamins
Vitamin E - Antisterility vitamin
• Alpha-tocopherol is the most active
biological form of Vitamin E
• tocopherol  Greek, promoter of childbirth
• functions in the body as an antioxidant in
that it inhibits the oxidation of unsat’d fatty
acids by O2
• Primary function: Antioxidant – protects
against oxidation of other compounds
Figure 7: Vitamin E structure

21. Fat-Soluble Vitamins
Vitamin K - Antihemorrhagic vitamin
• Vit K is synthesized by bacteria
that grow in colon
• Active in the formation of
proteins involved in regulating
blood clotting
• Deficiency may also occur
following antibiotic therapy that
sterilizes the gut which leads to
failure of blood clotting. (Classical
example of Count Covadango-
The son of King Alfonso of Spain,
google it)
Figure 8: Vitamin K structure

22. Thank you

23. Questions?