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:
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