ENZYMES

INTRODUCTION

-          The term enzyme was given by Wilhelm Kuhne to bio
       catalysts.

-          Major group of proteins are enzymes that are bio catalysts.

-          All enzymes are proteins, but all proteins are not enzymes.

-          Without enzymes no biological reaction would be possible.

-          Enzymes don’t alter chemical equilibrium.

-          All enzymes have word “ase” as their postfix.

-          Enzymes speed up biological reactions.

-          Example: - Carbonic anhydrase is an enzyme that enhances the
         dissolution rate of CO2 in water by 10^8 times.

                                          

-          Enzymes have an active site where substrate molecules attach.

Types of enzymes (based on site of action)

-          Endozymes: -

o   Produced in the cell.

o   Site of action is inside the cell itself.

o   Ex: - DNA polymerase.

-          Exozymes: -

o   Produced inside the cell.

o   Site of action is outside the cell.

o   Ex: - adrenaline.

Fischer’s lock and key model

-          Enzyme substrate union depends upon the reciprocal fit
         between the structure of enzyme and the structure of the
        substrate.

                                              

-          The substrate and active site of enzyme fit each other more or
         less like a lock and key.

-          The enzyme substrate union results in the release of energy.

-          The energy released helps the substrate molecule to attain
        activation energy.

-          In the activated state certain bonds of the enzyme-substrate
        complex become susceptible to cleavage.

                                        

-          This cleavage produces product and the enzyme remains
        unchanged.

Koshland’s induced fit model

-          Substrate induces geometric changes in the active site of the
       enzyme.

-          Enzyme molecule is made to fit completely in the active site of
      the substrate.

-          The hydrophobic and the charged group are involved in
       substrate binding.

-          Lysine and methionine are the two amino acids that are not
        involved in binding and catalysis.

Specificity of enzymes

-          Enzyme binds only to its substrate.

-          Enzymes have highly specific structure.

                                                     

-          Enzymes are specific towards cis and trans forms.

-          Enzymes are very sensitive towards temperature, pressure and
      pH.

-           

Enzyme reaction rates

-          Enzymes bind to substrates and convert them into products.

-          Most of the enzymes are produced in an inactive form called
       zymogen, these zymogen are acted upon by molecules that
       reactivate the enzyme.

-          The velocity of the enzyme catalysed reaction depends upon
        the substrate concentration.

                                                       

-          But at a certain level the enzyme is completely saturated with
       substrate so the velocity reaches a maximum point and don’t
       increase with further addition of substrate.

Applications of enzymes

-           Used in wine production.

-          Making cheese (rennin).

-          Candy production (invertase).

                                   

-          Bread whitening (lipoxygenase).

-          Meat tenderization (papain and ficin).