enzymes and vitamins

Enzymes and Vitamins

M. Faisal Shahid and Humaira Faraz (Ph.D.)

PCMD, ICCBS, University of Karachi.

• 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.

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 inaddition to a protein part.1. Apoenzyme: Protein part; inactive

alone2. Co-factor: Non-protein part:If organic: Termed coenzyme /co-substrate. If inorganic: Moiety/ Activator

• Apoenzyme + cofactor = Holoenzyme

Figure 2: Enzyme Anatomy

Classification of Enzymes

• According to function:– Type of reaction catalyzed– Identity of the substrate

• A substrate is the reactant in an enzyme-catalyzedreaction:– 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

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

Enzyme ClassificationEnzymes 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. LigasesReactions involving bond formation coupled with ATP hydrolysis

Table 1. Enzyme Classes

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


Enzyme Structure

Coenzymes / Cofactors


Enzyme Structure

Coenzymes / Cofactors

Inorganic CofactorsMetal Ion Enzymes

; Fe3+

Ca 2+

Cu2+

Fe2+

Mg2+

Mn2+K+

Zn2+

ThromboplastinTyrosinase, cytochrome oxidaseCytochrome oxidase, catalase, dehydrogenase Pyruvate kinaseArginase, pyruvate carboxylase, phosphatase, succinic dehydrogenase,

glycosyl transferases, cholinesterasePyruvate kinase

Carbonic anhydrase, carboxypeptidase, lactic dehydrogenase, alcohol dehydrogenase

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)

General Characteristics of Vitamins

Table 2: Enzyme Classification

Section 21.12


Table 3: Vitamin functions

Section 21.12


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 lesionsFragile blood vesselsLoose teeth and Bleeding gums

• Also Involved in metabolism of certain amino acids

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

The B Vitamins

Table 4: The Vitamin B Complex

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


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


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.


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


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


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

Thank you

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