Which property makes alanine aminotransferase (ALT) a MORE specific marker of hepatocellular damage than aspartate aminotransferase (AST)?
- A ALT is concentrated in the liver, whereas AST is also abundant in heart, skeletal muscle, kidney and brain ✓
- B ALT has a much longer plasma half-life than AST
- C ALT is located predominantly in the mitochondrial fraction of hepatocytes
- D ALT is released only when hepatocyte membranes are completely destroyed
Correct answer: A. ALT is concentrated in the liver, whereas AST is also abundant in heart, skeletal muscle, kidney and brain
Explanation
ALT is present almost exclusively in the cytosol of hepatocytes, so a raised ALT points strongly to liver injury. AST, in contrast, is distributed in cardiac muscle, skeletal muscle, kidney, brain and liver, and exists in both cytosolic and mitochondrial forms, so it rises in myocardial infarction, myositis and hemolysis as well. Half-life differences explain the timing of decline, not tissue specificity.
Reference: Harper's Illustrated Biochemistry, 31st ed.
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