ENZYMES

• Enzymes - are biomolecules which catalyzes biochemical reactions
• Enzymes - proteins with catalytic power colloidal, organic biocatalysts, that can catalyse and speed up chemical reactions.
• Enzymes

  • They are usually proteins.
  • They are known as “biological middle-men.”
• Enzymes are generaly named after adding the suffix “-ase” to the name of the substrate
• • Maltase acts on maltose
  • Nuclease act on nucleic acid
  • Proteases act on proteins
• Two Groups of enzymes can be recognized:

  1. ENDOENZYMES OR INTRACELLULAR ENZYMES
  2. EXOENZYMES OR EXTRACELLULAR ENZYMES
• ENDOENZYMES OR INTRACELLULAR ENZYMES – functioning inside the cell
• EXOENZYMES OR EXTRACELLULAR ENZYMES – produced inside the cell, excreted through the cell membrane, and function outside the cell, in the cell’s surrounding environment.
• Substrate – the substance by which the enzyme is acting on
• Coenzyme – a nonprotein organic molecule, frequently a B vitamin, that acts as a cofactor.
• Cofactor – a nonprotein portion of an enzyme that is necessary for catalytic function; examples are metallic ions such as Zn2+ and Mg2+.
• Apoenzyme – protein portion of the enzyme
• Prosthetic Group – the non-protein portion
• Active Site – pockets on the surface of the enzyme molecule where the substrate bind and where the reaction takes place
• Holoenzyme - apoenzyme + prosthetic group
• Inhibitor – substances that slows down enzymatic reactions.
• Allosteric Site – pockets on the surface of the enzyme where inhibitors or enzyme activators can bind.
• Characteristic of Enzymatic Reactions

  • Very specific
  • Highly effective
  • Biologically efficient
• Oxidoreductase – oxidation/reduction reaction
• Transferase – transfer of a group
• Hydrolase – hydrolysis reactions (breaking of bonds with the help of water to form two products)
• Lyase – removal or formation of double bonds
• Isomerase – rearrangement of atoms or bonds in the molecule
• Ligase/Synthetase – links two molecules to synthesize a product.
• Mechanism of Enzyme Action

  1. Lock and Key Model
  2. Induced Fit Model
  3. Michaelis-Menton Theory
• Factors Affecting Enzyme Action

  1. Enzyme and Substrate Concentration
  2. Temperature
  3. pH
  4. Presence of Inhibitor
  5. A. Competitive
  6. B. Non-competitive/Uncompetitive
• Type of Inhibitors

  1. Competitive Inhibitor
  2. Uncompetive/Non-competitive Inhibitor
• Enzyme Regulation

  1. Feedback Control
  2. Allosteric Control
  3. Proenzyme/Zymogen
  4. Covalent Modification of Proteins
  5. Isoenzyme
  6. Genetic Expression Induction
• Isoenzyme – formation of different isoforms of enzyme to different tissues of the body. They are obtained from different sources, differ from each other structurally, electrophoreticaly and immunologically but catalyse the same chemical reaction.
• Example of Isoenzyme:

  Glucose Transporters

  • brain – highest affinity to glucose
  • liver – low affinity
  • blood – low affinity
  • muscles – moderate affinity
• Example of genetic expression induction:

  • non-constitutive enzymes
  • antibodies
• Transition State Analogues

  • Have the same structure as the substrate in the ES complex
  • Have lower energy requirement compared to substrate|
  • Preferred by enzyme compared to substrate