Enzymes

Serum transaminases (ALT/AST)

• Hepatic enzymes that are usually intracellular, but are released from hepatocytes in context of hepatocellular injury
• Catalyze 𝛾-amino group transfers (amino acid metabolism)
• Often become deranged in all aetiologies
• Marked increase in hepatocellular pathologies
• Levels may or may not reflect the extent of damage and do not correlate with outcomes

Alanine aminotransferase (ALT)

• More sensitive than AST
• Predominantly cytosol located
• Predominantly in the liver
• Short half-life (circa 47 hours)

Aspartate aminotransferase (AST)

• In cytosol and mitochondria
• Present in liver, heart, pancreas, skeletal muscle, brain, lungs, RBCs, WBCs
• Short half-life (circa 17 hours)

Alkaline phosphatase (ALP)

• Enzymes that catalyze the hydrolysis of a number of organic phosphate esters
• Half-life of about one week – often lag to rise and slow precipitation in resolution of pathology
• Originates in epithelial cells of biliary ducts - synthesis and release is enhanced by cholestasis