An enzyme assay report states the activity as 50 IU/L. By international convention, one International Unit (IU) of enzyme activity corresponds to:

• A The amount of enzyme converting 1 mole of substrate per second
• B The amount of enzyme converting 1 millimole of substrate per hour
• C The amount of enzyme producing 1 gram of product per minute
• D The amount of enzyme converting 1 micromole of substrate per minute under specified conditions ✓

Explanation

One IU is defined as the enzyme quantity that transforms one micromole of substrate per minute under standardized assay conditions of temperature, pH, and substrate saturation. This practical unit remains standard in clinical laboratories even though the SI unit of catalytic activity is the katal, defined as conversion of one mole of substrate per second; note that 1 katal equals 60 million IU, making the katal inconveniently large for routine work. Mass-based definitions ignore catalytic activity, and millimole per hour is simply a wrong scale.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.