Enzymes

18Sep07
  • From the words “en zymo” (“from yeast”)
  • All enzymes are proteins, have globular structure
  • Average molecular mass from 104 – 106 Dalton
  • Classified into 6 classes, based on type of chemical reaction catalyzed by certain chemical reaction.
    • Oxidoreducterase
      • Catalyze oxidation-reduction reaction.
      • Example: CH3CH2(OH)COO (Lactate) + NAD+
        ó CH3C(O)COO (Pyruvate) + NADH + H+
    • Transferase
      • Catalyze transfer of substrates to the other.
      • Example: CH3(OH)CH(NH3)COO + THF ó CH2(NH3+)COO (Glucine) + THF(CH2)
    • Hydrolase
      • Catalyze cleavage of bonds by addition of substrate, eg H2O
      • Example: NH2CNH2(O) (Urea) + H2O ó CO2 + 2NH3
    • Lyaser
      • Catalyze cleavage of C-C, C-S and certain C-N bonds
      • Example: CH3C(O)COO (Pyruvate) à CH3CH(O)CO2 (Acetaldehyde)
    • Isomerase
      • Catalyze recognition of optical/geometry
      • Example: (CoA)C(O)CH2(CH3)COO- (Methylmalonyl-CoA) ó (CoA)C(O)CH2CH2COO (Succinyl-CoA)
    • Ligase (Syntatherase)
      • Catalyze formation of bonds between C & O,S,N occupied for hydrolysis of high energy phosphate
      • Example: CH3C(O)COO (Pyruvate) + CO2pyruvate carboxylase, ATP-> (COO)CH2C(O)COO

Nomenclature of Enzymes

  • There are some principles of nomenclature of the enzymes
    • Routine : Each enzyme has it’s own name (Eg: Ptyalin)
    • Trivial : Ending ‘-ase’ (Eg: Amylase)
    • Rational : The name of substrate, name of chemical reaction, type of chemical bond etc (Eg: 1,4-alpha-D-glucanohydrolase)
    • Numerical : Has it’s own number, the number of the class of enzyme, number of its subclass, number of sub-subclass, the order number within the sub-subclass (Eg: 3.2.1.1)

Structure of Enzyme

 

 

 

  • The shape of enzyme’s active site is so specific structure
  • Functions of active site:
    • Binding function (attachment process)
    • Catalytic function (chemically modified)

Radical Amino Acids of Charge Group

  • One substrate binds to enzyme with one/more chemical bond
  • Weak bonds
    • Hydrogen bonds
    • Ionic bonds etc
  • S (Substrate) + E (Enzyme) ó ES ó EP è E + P

Complex Enzymes

  • All enzyme can be classified as simple & complex enzymes
  • Complex enzymes
    • Protein (Apoenzymes, “Apo”=main protein)
    • Co-Factor
      • Mineral (Eg: Metal ions)
      • Organic
        • Coenzymes (Eg: NAD)
        • Prosthetic group (Eg: FAD)
  • Coenzymes which can be separated from apoenzyme by using electrolysis, binds at active site with weak bonds (easily separated)
  • Prosthetic group is hard to remove from enzyme because of strong bond
  • Organic cofactor can be classified into:
    • Vitamin containing cofactor
    • Non-vitamin containing cofactor

Vitamins

  • The small molecular mass organic substance that cannot be synthesized in the body but needed in metabolic process
  • 3 sources of vitamins
    • In diet (Eg: food)
    • Product of bacterial metabolism in intestines
    • Pharmaceutical preparations (supplements)
  • Some vitamins can be accumulated in tissue
    • Fat soluble vitamin (A,D,E,K) : accumulate in lipid-rich tissue such as liver, adipose tissue
  • Vitamin B12 & C are water soluble
  • Functions of vitamins:
    • Cofactor of catalytical functions
    • Cosubstrate: as additional substrate of chemical reaction (Eg: VitC)
    • Hormon-like function: such as VitD (steroid like: VitA)
    • Antioxidant: Protect the body tissue from abnormal radiating process (VitE : strongest. VitD, VitA, VitK, VitC)
    • Inhibitory: VitP (regulate the permeability of substance through membrane)
    • Photoreceptor: VitA

Mechanism of catalytic action of enzymes

  • Enzyme can only accelerate chemical reaction
  • The general character of catalytic action of enzyme:
    • Enzymes cannot initiate & generate chemical reaction but only accelerate them
    • Enzymes cannot change the direction of reversible reaction, but only accelerate the moment of establishment of an equilibrium state of the reaction
    • Enzymes accelerate chemical reaction because of decreasing in the level of activation energy
      • Activation Energy: It’s additional energy in comparison with the mean energy of a system which is required for the activation of the all substrates molecular (transitional state)
      • Steady state: Equal state between the formation of ES complex and its dissociates. Under this state, ES is constant.


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