Enzymes

• Enzymes


  Biological proteins that catalyze biochemical reactions
• Enzymes


  • Not consumed or changed in composition
  • Found in all body tissues
  • Increased in serum after cell injury
• Functions of enzymes


  • Hydration of carbon dioxide (respiration)
  • Nerve induction
  • Muscle contraction
  • Nutrient degradation
• Zymogen or proenzyme


  Inactive enzyme precursor (coagulation cofactors, digestive enzymes). Resting state ex gastric enzyme
• Terms associated with enzymes

  • Growth and reproduction
  • Energy storage and use
• Active site


  Cavity of an enzyme where the substrate binds and undergo chemical reaction
• Allosteric site


  A cavity other than the active site that binds the regulatory molecule (effector)
• Substrate


  Substance acted upon by enzymes specific for each of their particulate enzyme
• Cofactor


  Non protein substance added in enzyme substance complex to manifest the enzyme activity
• Two types of cofactors

  • Coenzyme or prosthetic group
  • Activator
• Classification of enzymes


  • Oxidoreductase
  • Transferase
  • Hydrolase
  • Isomerase
  • Ligase
  • Lyases
• Isoenzyme


  Enzymes of similar enzymatic activity but differs in physical, biochemical and immunologic characteristic
• Apoenzyme


  Protein portion of the enzyme subject to denaturation in which it loses its activity. Sometimes, enzyme in inactive form, needed a co-factor to get activated.
• Holoenzyme


  Active enzyme or substrate formed by combination of a coenzyme and an apoenzyme
• Types of enzyme kinetics

  • First order kinetics
  • Zero order kinetics
• Factors that influence enzymatic reaction

  • Substrate concentration
  • Enzyme concentration
  • pH
  • Temperature
• Competitive inhibitor


  Binds to active site (reversible)
• Non-competitive inhibitor


  Does not bind to the active site but to the allosteric site
• Uncompetitive inhibitor


  Binds to enzyme-substrate complex
• Activator


  Metallic (Ca) or Non-metallic (Cl)
• Cofactor


  Coenzymes (prosthetic group) or Secondary substrate (NAD)
• General methods of measuring enzymatic reactions

  • Fixed time
  • Continuous time
• Enzyme quantitation


  • Photometric
  • Increase in product concentration
  • Decrease concentration
  • Increase in concentration of altered coenzyme
• MI (Myocardial Infarction) profile

  • Creatinine Kinase (CK)
  • Aspartate Aminotransferase (AST)
  • Lactate Dehydrogenase (LDH)
• Creatinine Kinase (CK)


  Storage of high energy creatinine phosphate in muscle cells. Highest activity is in skeletal muscle, heart and brain tissue. Used to assess Myocardial Infarction
• CK isoenzymes


  • CK-1 (CK-BB) Brain Type
  • CK-2 (CK-MB) Hybrid Type
  • CK-3 (CK-MM) Muscle Type
  • Macro-CK
  • Mitochondrial-CK
• Aspartate Aminotransferase (AST)


  Involved in synthesis and degradation of amino acids. Formerly SGOT (Serum Glutamic-Oxaloacetic transaminase). Major clinical uses: Myocardial Infarction, Hepatocellular Disorders
• De Ritis ratio (AST/ALT)

  <1 acute disorders of the liver, acute viral hepatitis, infectious mononucleosis

  >1 chronic disorders of the liver, alcoholic liver disease, post-necrotic cirrhosis, chronic active hepatitis
• Lactate Dehydrogenase (LDH)


  Widely distributed, most non-specific enzyme. Highest activity in heart, hepatic, skeletal muscle, and RBC. Increased levels are seen in cardiac disease, hepatic diseases, skeletal diseases, renal diseases, and megaloblastic anemia
• Liver enzymes


  • Alanine Aminotransferase (ALT)
  • Alkaline Phosphatase (ALP)
  • Gamma-Glutamytransferase (GGT)
  • Lactate Dehydrogenase (LD)
• Alanine Aminotransferase (ALT)


  Formerly Serum Glutamic-pyruvic Transaminase (SGPT). Similar activity to AST, catalyzes transfer of an amino group from alanine to a-ketoglutarate with the formation of glutamate and pyruvate. Distributed in many tissues, highest concentration in the liver.
• Alkaline Phosphatase


  Catalyze hydrolysis of phosphoesters. Cleaves phosphate group of the phosphomonoesters producing phosphate ion. Not specific, can react with many different substrates. More active in an alkaline pH. Requires Mg.
• Lactate Dehydrogenase

  Highest levels are seen in Pernicious Anemia and Hemolytic Disorders, Marked elevations are also seen in Lymphoblastic Leukemia
• Anemia as a marker for Acute Myocardial Infarction


  Rise: 12-24 hours, Peak: 48-72 hours, Return to normal: 10 days (best indicator for delayed check-ups due to chest pain)
• Aspartate Aminotransferase (AST)


  Similar activity to ALT, catalyzes transfer of an amino group from alanine to a-ketoglutarate with the formation of glutamate and pyruvate, Distributed in many tissues, highest concentration in the liver
• Alanine Aminotransferase (ALT)


  Formerly known as Serum Glutamic Pyruvic Transaminase (SGPT), More liver specific enzyme among the transaminases, Used to evaluate hepatic disorders (ALT elevations are higher than AST), Cardiac tissue contains small amount of ALT activity
• Alkaline Phosphatase (ALP)


  Catalyzes hydrolysis of phosphoesters, Cleaves phosphate group of the phosphomonoesters producing phosphate ion, Not specific, can react with many different substrates, More active in an alkaline pH, Requires Mg activator, Used in the evaluation of hepatobiliary and bone disorders
• Alkaline Phosphatase Isoenzymes


  • Liver ALP isoenzymes
  • Placental ALP enzyme
  • Intestinal ALP isoenzyme
  • Bone ALP isoenzymes
• Lactate Dehydrogenase (LD)


  Electrophoresis shows 5 isoenzymes (LD-1 to LD-5), LD-1 is the fastest and most anodal, LD-5 is the slowest and most cathodal, Normal isoenzyme concentration is LD2 > LD1 > LD3-LD4 > LD5, Flipped pattern (LD1 > LD2) is diagnostic for Acute Myocardial Infarction, Intravascular Hemolysis, and Hemolyzed Specimen
• Abnormal Alkaline Phosphatase Isoenzyme Fractions

  • Carcinoplacental ALP
  • Regan Variant
  • Nagao