Enzymology

• precursor of a product in an enzymatic reaction binds to the active site of the enzyme

  Substrate
• Greek word "Enzymos" - leavened named by Kuhne to the molecules detected by Eduard Buchner

  Enzymes
• • Biocatalysts
  • Protein in nature
  • Found in all body tissues
  • Large molecules, normally within cells
  • Very specific, targeting only one specific reacting species


  Enzymes
• • alter the rate of chemical reaction

  affects only the rate equally on both directions


  Catalysts
• whole enzyme molecule

  Holoenzymes
• protein portion of enzyme

  Apoenzyme
• apoenzyme + metal ion cofactor


  Metalloenzyme
• non-protein portions

  Cofactors
• organic cofactors; acts as transient carriers of specific functional groups

  Coenzymes
• inorganic cofactors; can be metallic or non-metallic

  Activators
• when a coenzyme or metal ion is very tightly or even covalently bound to the enzyme protein


  Prosthetic group
• NAD/NADH or NADP/NADPH

  Dehydrogenase reactions
• Cysteine 


  Creatine kinase
• Pyridoxal (Vitamin B6) phosphate


  Transaminase reaction
• 1. NAD/NADH or NADP/NADPH
  2. Cysteine
  3. Pyridoxal (vit B6)


  Coenzymes
• 
  

  • Metallic
  • Non-metallic

  Coenzymes
• • Calcium (Amylase)
  • Magnesium (CK)
  • Zinc (LDH)
  • Iron
  • Manganese
  • Copper

  Metallic
• Components of an enzyme:

  1. Active site
  2. Allosteric site
• is a water-free cavity, where the substrate interacts with particular charged amino acid residues


  Active Site
• is a cavity other than the active site; may bind regulator molecules


  Allosteric Site
• • inactive forms of enzymes
  • digestive enzymes are produced in its inactive form originally secreted from organ of production
  • examples: pepsinogen and plasminogen

  Proenzymes / Zymogens
• enzymes that catalyze the same reaction but differ in terms of physical or chemical characteristics, tissue distribution as well as electrophoretic mobility

  Isoenzymes
• Isoenzymes

  • LDH - LD1, LD2, LD3, LD4, LD5
  • CK - CKMM, CKMB, CKBB
  • ACP - prostatic and erythrocytic ACP
• 1. Macroenzyme type 1 - enzyme bound to an immunoglobulin
  2. Macroenzyme type 2 - enzyme bound to non-immunoglobulin substance


  Types of macroenzymes
• • are high-molecular mass forms of the serum enzymes
  • larger enzymes leads to decreased clearance of enzymes in circulation
  • enzymes bound to immunoglobulin have longer half-life
  • examples: macro-CK, macroamylase

  Macroenzymes
• 1. Emil Fischer's/Lock and Key Theory - premise that the shape of the key (S) must fit into the lock (E)
  2. Kochland's/Induced Fit Theory - substrate binding to the active site of the enzyme


  Enzyme Theory
• • enzymes catalyze physiologic reactions by lowering the activation energy level that the substrate must reach for the reaction to occur
  • act by decreasing activation energy required for the biochemical reaction to push through


  Enzyme Kinetics
• reaction rate is directly proportional to substrate concentration


  First order reaction
• reaction rate depends only on enzyme concentration


  Zero order reaction
• • the higher the substrate concentration, the more substrate bound to enzyme and the greater the rate or velocity of the reaction
  • when all enzyme is bound to substrate, there will be no further increase in velocity
  • when substrate is present in an adequate amount, the rate of reaction depends only in enzyme concentration

  Michaelis-Menten
• when an enzyme combines with only one substrate and catalyzes only one reaction

  Absolute specificity
• when enzymes combine with all substrate with a particular chemical group

  Group specificity
• when enzymes reacting with specific chemical bonds

  Bond specificity
• predominantly combine with only one optical isomer of a certain commpound

  Stereospecificity
• E+S > ES > P

  Enzyme Reaction
• 1. pH
  2. Temperature
  3. Enzyme Concentration
  4. Substrate Concentration
  5. Inhibitors
  6. Cofactors
  7. Isoenzymes
  8. Storage
  9. Ionic Strength or Electrolyte
  10. Hemolysis
  11. Lactescence

  Factors Affecting Enzymatic Reactions
• • most reactions occur at pH 7.0
  • some in alkaline: ALP
  • some in acidic: ACP and pepsin

  pH
• • 37-38 degree Celsius; optimum temperature
  • 25'C, 30'C, and 37'C - enzyme activity


  Temperature
• increased reaction velocities

  Increased temperature
• decrease enzyme activity

  Decreased temperature