ENZYMES

• Enzyme


  Compound, usually a protein, that acts as a catalyst for a biochemical reaction
• Enzymes are not consumed in the reactions
• Enzymes

  • Most enzymes are globular proteins
  • Enzymes are the most effective catalysts known
  • Few enzymes are now known to be ribonucleic acids (RNA)
  • Enzymes undergo all the reactions of proteins including denaturation
• Enzyme activity

  Measure of the rate at which an enzyme converts substrate to products in a biochemical reaction
• Simple enzyme


  Enzyme composed only of protein (amino acid chains)
• Conjugated enzyme


  Enzyme that has a nonprotein part in addition to a protein part
• Apoenzyme


  Protein part of a conjugated enzyme
• Cofactor


  Nonprotein part of a conjugated enzyme
• Holoenzyme


  Biologically active conjugated enzyme produced from an apoenzyme and a cofactor
• Coenzyme


  Small organic molecule that serves as a cofactor in a conjugated enzyme
• Coenzymes are synthesized within the human body using building blocks obtained from other nutrients
• Many cofactors are permanently bonded, via covalent bonds, to the amino acid portion of an enzyme
• Substrate


  Reactant in an enzyme-catalyzed reaction; the substance upon which the enzyme "acts"
• Three important aspects of the naming process

  • The suffix -ase identifies it as an enzyme
  • Type of reaction catalyzed by an enzyme is often used as a prefix
  • Identity of substrate is often used in addition to the type of reaction
• Major classes of enzymes

  • Oxidoreductase
  • Transferase
  • Hydrolase
  • Lyase
  • Isomerase
  • Ligase
• Oxidoreductase


  Enzyme that catalyzes an oxidation-reduction reaction
• Oxidation


  Losing of electron/s
• Reduction

  Gaining of electron/s
• Dehydrogenase


  Removal of hydrogen atoms
• Transferase


  Enzyme that catalyzes the transfer of functional group from one molecule to another
• Transaminases


  Catalyzes the transfer of an amino group from one molecule to another
• Kinases


  Catalyzes the transfer of phosphate group from ATP to give ADP and a phosphorylated product
• Hydrolase


  Enzyme that catalyzes a hydrolysis reaction in which the addition of a water molecule to a bond causes the bond to break
• Lyase


  Enzyme that catalyzes the addition of a group to a double bond or the removal of a group to form a double band in a manner that does not involve hydrolysis or oxidation
• Isomerase


  Enzyme that catalyzes the isomerization (rearrangement of atom) of a substrate in a reaction, converting it into a molecule isomeric with itself
• Ligase


  Enzyme that catalyzes the bonding together of two molecules into one with participation of ATP and water
• Active site


  Relatively small part of an enzyme's structure that is actually involved in catalysis
• Some enzymes have more than one active site
• Enzyme-substrate complex


  Intermediate reaction species that is formed when a substrate binds to the active site of an enzyme
• Lock-and-key model


  Enzyme has a pre-determined shape for the active site, only substrate of specific shape can bind with active site
• Induced-fit model


  Substrate contact with enzyme will change the shape of the active site, allows small change in space to accommodate substrate

  
• Forces that determine substrate binding

  • H-bonding
  • Hydrophobic interactions
  • Electrostatic interactions
• Enzyme specificity

  Extent to which an enzyme's activity is restricted to a specific type of substrates, a specific type of chemical bond, or a specific type of chemical reaction
• Major types of enzyme specificity

  • Absolute specificity
  • Group specificity
  • Linkage specificity
  • Stereochemical specificity
• Absolute specificity


  An enzyme will catalyze a particular reaction for only one substrate, catalyzes only one reaction

  catalase – enzyme with absolute specificity.

  most restrictive of all specificities (not common).

  urease is an enzyme with absolute specificity.
• Group specificity


  Enzyme will act only on molecules that have a specific functional group, such as hydroxyl, amino, or phosphate groups
• Linkage specificity


  Enzyme that will act on a particular type of chemical bond, irrespective of the rest of the molecular structure

  Most general of enzyme specificities
• Stereochemical specificity


  Enzyme that acts on a particular stereoisomer, can distinguish between stereoisomers

  Chirality is inherent in an active site (amino acids are

  chiral compounds)
• Temperature

  Measure of the kinetic energy (energy of motion) of molecules
• Higher temperatures


  Molecules are moving faster and colliding more frequently