Enzymes

• Enzymes


  Biological catalysts that speed up metabolic reactions
• Enzymes


  • They are not changed by the reaction and can be reused
  • Some can make reactions happen many million times more quickly than they otherwise would
• Enzymes


  3D, tertiary, Globular proteins
• Activation energy


  Energy barrier that must be overcome before a reaction can take place
• Enzymes


  Lower the activation energy required to overcome the energy barrier, enabling reactions to take place at the rapid rate necessary to sustain life
• Enzyme action


  1. Substrate binding

  2. Transition state facilitation

  3. Catalysis

  4. Release
• Lock and Key model

  Enzyme active site is an exact match to the shape of the substrate
• Induced Fit model


  Active site can mould itself around the substrate, forming a precise fit
• Cofactors


  Non-protein substances that enzymes require in order to function
• Prosthetic groups


  A type of cofactor
• Coenzymes


  A particular type of cofactor, non-protein organic molecules necessary for enzyme action
• Substrate and enzyme concentration


  Affect the rate of enzyme activity
• Temperature


  Affects enzyme activity
• pH


  Affects enzyme activity
• Competitive inhibition


  Inhibitor substance competes with usual substrate for the active site
• Non-competitive inhibition


  Inhibitor attaches to part of enzyme other than active site, changing its shape
• Competitive inhibition


  Inhibitor (malonic acid/malonate) has a very similar molecular shape to the substrate (succinate), reducing the activity of the enzyme (succinate dehydrogenase)
• Non-competitive inhibition


  Inhibitor attaches to a part of the enzyme other than the active site (allosteric), changing the shape of the active site so it is no longer complementary to the substrate
• In non-competitive inhibition, an increase in substrate concentration does not reduce the effect of the inhibitor
• Allosteric enzymes


  Enzymes that have a second site where (non-substrate) molecules can attach
• When enough products have been produced for the cells' needs


  The product (or another molecule linked to the product) can join the allosteric site of the enzyme and effectively act as a non-competitive inhibitor, reducing enzyme activity above and beyond the cells' needs
• Some inhibitors are irreversible, their effects cannot be reversed and the enzyme is permanently damaged
• Cyanide is a non-reversible inhibitor of the respiratory enzyme cytochrome oxidase
• Enzymes as biomarkers of disease


  The presence of certain enzymes can be used as a diagnostic tool to confirm a particular disease, and monitoring enzyme levels can track disease progression or recovery
• Elastase


  An enzyme released by white blood cells as part of the immune response to lung infection, which breaks down bacterial pathogens and the protein elastin in lung tissue
• Cigarette smoke causes excess elastase release


  Not enough elastase inhibitor (alpha-1-antitrypsin) is present to control the elastase, resulting in elastin breakdown and emphysema
• Often it is not the enzymes themselves that are monitored as biomarkers, but the proteins they produce
• Enzyme inhibitors as therapeutic drugs


  Specific enzyme inhibitors can target enzymes involved in disease progression to reduce or stop disease
• Effective enzyme inhibitors as therapeutic drugs


  • Specific to the target enzyme
  • Able to work at low doses to avoid toxicity
• Therapeutic enzyme inhibitors


  • ALAT to reduce effects of lung infection elastase
  • ACE inhibitors to treat high blood pressure and cardiovascular conditions
  • Penicillin and other antibiotics to inhibit bacterial cell wall formation enzymes
  • Antiviral drugs to inhibit viral DNA/RNA polymerases
• Current research includes developing enzyme inhibitors with a complementary shape to block the active sites of enzymes involved in disease progression
• Immobilised enzymes


  Enzymes trapped within or attached to appropriate inorganic or organic materials to maximise efficiency
• Methods of enzyme immobilisation

  • Adsorption
  • Entrapment
  • Encapsulation
  • Cross-linkage
• Advantages of enzyme immobilisation

  • Enzymes are thermostable and effective over a wider temperature range
  • Enzymes are more resistant to changes in pH
  • Enzymes can be retained and reused
  • Processes can be continuous, faster and produce less waste
  • No contamination of end product with enzymes
• Diagnostic reagent strips as biosensors

  Enzymes used to identify and quantify specific molecules, causing a colour change or electrical signal
• Diagnostic reagent strip applications

  • Glucose monitoring
  • Pregnancy testing
  • Identifying cardiovascular disorders and pre-eclampsia
• Enzyme inhibitors are increasingly being used in diagnostic reagent strips to capture the enzyme being monitored and give a positive readout
• Adsorption: enzymes are attached by weak forces to and inert substance such as a matrix
• Entrapment: enzymes are trapped within polymers such as sodium alginate beads
• Encapsulation : enzymes are trapped inside a selectively permeable membrane such as nylon