3. Which statement best explains why alanine aminotransferase (ALT) is more specific than aspartate aminotransferase (AST) for hepatocellular injury? (A) ALT is located exclusively in hepatocyte mitochondria (B) AST has a longer plasma half‑life than ALT (C) ALT is predominantly cytosolic and has limited expression in extrahepatic tissues (D) ALT requires pyridoxal phosphate, whereas AST does not

5. An enzyme shows strong substrate specificity, yet mutation of a single active‑site residue leads to a dramatic increase in catalytic rate but a decrease in substrate affinity. Which interpretation best fits this observation? (A)The mutation stabilizes the enzyme–substrate complex but destabilizes the transition state (B)The mutation decreases the activation energy but weakens binding interactions in the active site (C)The mutation increases both kcat and KM by stabilizing the transition state (D)The mutation eliminates a key catalytic group but improves substrate recognition

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