One international unit (IU) of enzyme activity in a clinical laboratory assay is defined as the amount of enzyme that:

• A Produces 1 mole of product per second, corresponding to one katal
• B Doubles the reaction rate relative to a blank control
• C Converts 1 millimole of substrate per hour at standard temperature and pressure
• D Converts 1 micromole of substrate to product per minute under specified conditions ✓

Explanation

The traditional international unit equals 1 micromole of substrate transformed per minute under defined assay conditions of temperature and pH, which is how serum enzyme results remain reported worldwide. The SI unit, the katal, corresponds to 1 mole per second, so 1 katal equals 60 million IU; option A confuses the two systems. Rate doubling relative to a blank has never been part of the definition.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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