AST AND ALT

• Aspartate Aminotransferase/Transaminase (AST)
• This enzyme is involved in the transfer of an amino group between aspartate and a-keto acids with the formation of oxaloacetate and glutamate.

  AST
• Reactant of AST Assay:

  • aspartate + a-ketoglutarate >AST< - oxaloacetate + glutamate
• What is the coenzyme required for the AST assay?

  pyridoxal phosphate
• What is the other or previous name of Aspartate Aminotransferase?

  serum glutamic-oxaloacetic transaminase
• What are the 2 isoenzyme fractions of AST?

  cytosolic/cytoplasmic

  mitochondrial
• cAST: cytoplasmic aspartate aminotransferase
• mAST: mitochondrial aspartate aminotransferase
• What is the predominant form of isoenzyme fractions present in the serum?

  cytoplasmic isoenzyme
• Ranking of AST in the body: Highest Concentrations

  1. Cardiac tissue
  2. Liver
  3. skeletal muscle
• Lowest concentration of AST in the body are found:

  • Kidney
  • Pancreas
  • RBC
• Clinical significance of AST

  • Myocardial infarction
  • hepatocellular disorders
  • skeletal muscle involvement
• During Myocardial infarctions, AST rises after 6 to 8 hours
• During Myocardial infarctions, AST peaks at 24 hours
• During Myocardial infarctions, AST normalizes within 5 days
• Pronounced AST levels conditions : 5 times the NORMAL
• Pronounced AST levels conditions

  • acute hepatocellular damage
  • myocardial infarction
  • circulatory collapse
  • acute pancreatitis
  • infectious mononucleosis
• Moderate AST levels conditions : 3 to 5 times the NORMAL
• Moderate AST level conditions

  • biliary tract obstruction
  • cardiac arrhythmias
  • congestive heart failure
  • metastatic or primary tumor in the liver
  • muscular dystrophy
• Slight AST levels conditions: up to 3 times the NORMAL
• Slight AST level conditions

  • pericarditis
  • cirrhosis
  • pulmonary infarction
  • delirium tremens
  • cerebrovascular accident
• Specimen consideration

  • Hemolysis should be avoided because it can dramatically increase serum AST concentration
  • AST activity stable in serum for 3 to 4 days at refrigerated temperature
• Methodologies for AST

  • Karmen: Coupled Enzymatic
  • Diazonium
  • Reitman-Frankel: Colorimetric
• This enzymatic method for AST determination is a coupled enzymatic reaction using AST and MD.

  Karmen Method
• Assay reaction of AST:

  aspartate + alpha ketoglutarate <-> oxaloacetate + glutamate
• Indicator reaction of AST:

  oxaloacetate + NADH <-> malate + NAD+
• In Karmen-Method: The measure of loss of absorbance at 340 nm due to formation of NAD+
• What is the optimal pH for AST assay?

  7.3 to 7.8
• Diazonium salt

  • formation of diazonium derivative
• What is the reagent used in the Reitman-Frankel Method for AST determination?

  dinitrophenylhydrazone
• What is the endpoint for Reitman-Frankel Method?

  formation of blue color
• What is the absorbance of the endpoint for the Reitman-Frankel Method?

  505 nm
• Disadvantage of Reitman-Frankel Method

  • lacks specificity
  • reacts with any keto-compound
• Alanine Aminotransferase/Transaminase (ALT)
• What is the other name of Alanine Aminotransferase?

  serum glutamic-pyruvic transaminase (SGPT)
• This has enzymatic activity similar to AST?

  ALT
• This enzyme catalyzes transfer of amino group from alanine to alpha-ketoglutarate with formation of glutamate and pyruvate ?

  Alanine Aminotransferase
• The highest concentration of ALT is major in what tissue?

  Liver
• ALT is more liver-specific than AST
• Order ALT in the body

  1. Liver
  2. Kidney
  3. myocardium
  4. skeletal muscle
  5. pancreas
  6. spleen
  7. RBCs