Question:
Which of the following liver enzymes is predominantly mitochondrial?
Which of the following liver enzymes is predominantly mitochondrial?
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This transaminase has both cytosolic and mitochondrial isoenzymes.
Updated On: Jun 24, 2026
- SGOT (AST)
- SGPT (ALT)
- GGT
- 5'-Nucleotidase
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The Correct Option is A
Solution and Explanation
Step 1: Recall the subcellular location of the transaminases. AST (aspartate aminotransferase, SGOT) exists in two isoforms: a cytosolic form and a mitochondrial form, with a large fraction of hepatic AST being mitochondrial. ALT (alanine aminotransferase, SGPT) is almost entirely cytosolic.
Step 2: Apply the clinical correlate. Because AST has a major mitochondrial pool, conditions that cause deep cellular and mitochondrial injury, such as alcoholic hepatitis, release more AST, contributing to the AST:ALT ratio greater than 2 seen in alcoholic liver disease. ALT, being cytosolic, is the more liver-specific marker but is not mitochondrial.
Step 3: Place the other enzymes. GGT (gamma-glutamyl transferase) is a membrane-bound enzyme of the canalicular and microsomal membranes, not mitochondrial. 5'-Nucleotidase is a plasma membrane-bound enzyme, again not mitochondrial.
Step 4: Since AST is the enzyme with a predominant mitochondrial isoform among the choices, the answer is SGOT/AST (option A).
Step 2: Apply the clinical correlate. Because AST has a major mitochondrial pool, conditions that cause deep cellular and mitochondrial injury, such as alcoholic hepatitis, release more AST, contributing to the AST:ALT ratio greater than 2 seen in alcoholic liver disease. ALT, being cytosolic, is the more liver-specific marker but is not mitochondrial.
Step 3: Place the other enzymes. GGT (gamma-glutamyl transferase) is a membrane-bound enzyme of the canalicular and microsomal membranes, not mitochondrial. 5'-Nucleotidase is a plasma membrane-bound enzyme, again not mitochondrial.
Step 4: Since AST is the enzyme with a predominant mitochondrial isoform among the choices, the answer is SGOT/AST (option A).
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