Which biochemical property makes alanine aminotransferase (ALT) a more specific marker of hepatocellular injury than aspartate aminotransferase (AST)?
- A ALT is concentrated almost exclusively in the cytosol of hepatocytes, whereas AST is abundant in heart, skeletal muscle, kidney, brain and red cells ✓
- B ALT has a longer plasma half-life than AST
- C ALT is released only after mitochondrial rupture, giving a delayed but specific signal
- D ALT is cleared exclusively by the kidney, so its level reflects hepatic release alone
Correct answer: A. ALT is concentrated almost exclusively in the cytosol of hepatocytes, whereas AST is abundant in heart, skeletal muscle, kidney, brain and red cells
Explanation
ALT is present almost solely in the cytosol of hepatocytes, so a raised serum ALT points strongly to liver cell injury. AST, in contrast, occurs in the cytosol and mitochondria of liver, cardiac muscle, skeletal muscle, kidney, brain and erythrocytes, so it rises in myocardial infarction, myositis and haemolysis as well. The half-life difference does exist but is not the basis of specificity, and ALT is released from cytosol, not mitochondria.
Reference: Harper's Illustrated Biochemistry, 31st ed.
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