ENZYMES

• Enzyme


  A compound, usually a protein, that acts as a catalyst for a biochemical reaction
• Enzymes


  • Cause cellular reactions to occur millions of times faster
  • Not consumed during the reaction but merely help the reaction occur more rapidly
  • Mostly are globular proteins
• Types of enzymes


  • Simple enzyme (composed only of protein)
  • Conjugated enzyme (has a non-protein part in addition to a protein part)
  • Apoenzyme (protein of the conjugated enzyme)
  • Cofactor (non-protein part of the conjugated enzyme)
  • Holoenzyme (biochemically active conjugated enzyme produced from an apoenzyme and a cofactor)
  • Coenzyme (serves as a cofactor in a conjugated enzyme)
• Nomenclature and classification of enzymes

  • Named about the function of the enzyme, type of reaction catalyzed and the substrate identity
  • Substrate (reactant in an enzyme-catalyzed reaction)

  
• 3 important aspects in the naming process of enzymes

  • Suffix (most enzymes end in the suffix "ase")
  • Type of reaction catalyzed by an enzyme is often used as a prefix
  • Identity of substrate and type of reaction catalyzed
• Classification of enzymes

  • Oxidoreductase (catalyzes an oxidation-reduction reaction)
  • Transferase (catalyzes the transfer of a functional group from one molecule to another)
  • Hydrolase (catalyzes the hydrolysis reaction)
  • Lyase (catalyzes the addition of a group to a double bond or the removal of a group to form a double bond in a manner that does not involve hydrolysis or oxidation)
  • Isomerase (catalyzes the isomerisation of a substrate in a reaction converting it to a molecule isomeric with itself)
  • Ligase (catalyzes the bonding together of two molecules into one with the participation of ATP)
• Enzyme active site


  Small part of an enzyme's structure that is actually involved in catalysis
• Enzyme-Substrate Complex


  The intermediate reaction species that is formed when a substrate binds to the active site of an enzyme

  
• Lock-and-Key Model


  Active site in the enzyme has the fixed, rigid geometrical conformation and the substrate with a complementary geometry can be accommodated

  
• Induced-Fit Model


  Enzyme's active site is not rigid and static, there's a constant change in shape to accommodate the incoming substrate

  
• Enzyme Specificity


  The extent to which an enzyme's activity is restricted to a specific substrate, a specific group of substrate, a specific type of chemical bond, or a specific type of chemical reaction
• Types of Enzyme Specificity

  • Absolute Specificity (catalyze only one reaction)
  • Group Specificity (act only on molecules that have a specific functional group)
  • Linkage Specificity (act on the particular type of bond, irrespective to the rest of the molecular structure)
  • Stereochemical Specificity (act on a particular isomer)

  
• Enzyme Activity


  Measures the rate at which an enzyme converts substrate to products in a biochemical reaction

  
• Factors that affect enzyme activity

  • Temperature
  • pH
  • Substrate Concentration
  • Enzyme Concentration
• Optimum temperature


  Temperature at which an enzyme exhibits maximum activity

  
• Optimum pH


  pH at which an enzyme exhibits maximum activity
• Turnover number


  Number of substrate molecules transformed per minute by one molecule of enzyme under optimum conditions of temperature, pH and saturation
• Extremozymes


  Microbial enzymes active at conditions that would inactivate human enzymes and enzymes present in other types of higher organisms
• Types of Extremophiles


  • Acidophiles (optimal growth at pH levels of 3.0 or below)
  • Alkaliphiles (optimal growth at pH levels of 9.0 or above)
  • Hyperthermophiles (temperature between 80°C and 122°C needed to thrive)
  • Halophiles
  • Cryophiles
• Enzyme Inhibitor


  Substance that slows or stops the normal catalytic function of an enzyme by binding to it
• Types of Enzyme Inhibition

  • Reversible Competitive Inhibition
  • Reversible Non-Competitive Inhibition
  • Irreversible Inhibition
• Reversible Competitive Inhibition


  Competitive enzyme inhibitor (molecule that sufficiently resembles an enzyme substrate in shape and charge distribution that it can compete with the substrate for occupancy of the enzyme's active site)
• Reversible Non-Competitive Inhibition


  Non-competitive enzyme inhibitor (molecule that decreases enzyme activity by binding to a site on an enzyme other than the active site)
• Irreversible Inhibition


  Irreversible enzyme inhibitor (molecule that inactivates enzyme by forming a strong covalent bond to an amino acid side-chain group at the enzyme's active site)
• Allosteric Enzyme


  Enzyme with quaternary structure (2 or more protein chains) and 2 kinds of binding sites (for substrates and for regulators)

  
• Positive Regulator


  Substance that binds at the regulatory sites of allosteric enzymes and increases enzyme activity
• Negative Regulator


  Substance that binds at the regulatory sites of allosteric enzymes and decreases enzyme activity
• Feedback Control


  A process in which activation or inhibition of the first reaction in a reaction sequence is controlled by a product of reaction sequence
• Proteolytic Enzymes


  Enzymes that catalyze the breaking of peptide bonds that maintain the primary structure of protein
• Zymogen


  Inactive precursor of a proteolytic enzyme
• Covalent Modification of Enzyme


  Process in which enzyme activity is altered by covalently modifying the structure of the enzyme through attachment or removal of a chemical group

  
• Phosphorylation


  Process of addition of the phosphate group to the enzyme by protein kinases
• Dephosphorylation


  Removal of the phosphate group from the enzyme by phosphatases
• Enzymes are used to diagnose certain diseases and in the treatment of disease