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Current Category » Bio-chemistry

Enzymes

Definition of Enzyme:

Catalytically active protein of biological origin or organic catalyst produced by living cells

Substrate: Substance upon which an enzyme acts.

Classification of Enzyme (IUD System, 1961):

Based on Type of Reaction Enzyme is classified as below:
 
1) Oxidoreducctase (Dehydrogenases):

Reaction catalyzed - Biological oxidation- reduction- ex. Pyruvie oxireductase, Ascorbic oxidase, succinic dehydrogenase, cytochrome oxidase.

2) Transferases (Transaminase):

Ex. Transketolase, Transmethylase,Reaction catalyzed: Transfer of groups.

3) Hydrolases: Ex- Lipases, urease, pepsin, amylase, cholinesterase.Reaction catalyzed - Hydrolysis

4) Lyases (Decarboxylases):  Ex. carboxylases, aldolases, fumarase.Reaction catalyzed - catalyzed removal of groups

5) Isomerases: Ex. triose phosphate isomerase, epimerase, alanine racemase.Reaction catalyzed – Catalyse conversion to other isomeric form.
 
6) Ligases or synthetases: Ex. Succinic thiokinase, Glutamine synthetase.Reaction catalyzed – catalyse linking together of two compounds.

Mechanism of Enzyme Action:

The enzyme combines with the substance on which it acts (substrate) to form an enzyme substrate complex called Michaelis complex

E+S          → ES

Enzyme is liberated and the substrate is broken into the products of the reaction

ES            →   E + P (products)

Active Site: The region of an enzyme surface that binds the substrate molecule and catalytically transforms it.

Functional Groups Present at the Active Site:

Amino acids such as aspartic acid, glutamic acid, lysine, serine etc. the side chain groups - COOH, - NH2, -CH2OH etc. serve as catalytic groups at active site.

Fischer's Lock and Key Model:

Activation energy with and. without enzyme

Chemical Nature of Enzyme:

All enzymes are protein in nature without any exception. Most enzymes contain protein and non-protein groups.
 
Enzyme → Protein + Non Protein
Holoenzyme → Apoenzyme + Cofactor

Cofactors may be divided into three groups

1) Prosthetic Group e.g. Porphyrin
2) Coenzyme e.g. NAD; NADP +
3) Metal Activators e.g. K+, Mn2+, Mg+, Zn2+ etc.

Factors Affecting Enzyme Activity:

1) PH
2) Temperature
3) Substrate Concentration
4) Enzyme Concentration
5) Concentration of any Activator Present
6) Concentration of any Inhibitor Present
7) Ionic Strength
8) Redox Potential
9) Concentration or Reaction Products

 

Current Category » Bio-chemistry