19. A single subunit enzyme converts 420 μmoles of substrate to product in one minute.
The activity of the enzyme is __________ × 10−6 Katal.
The enzyme activity is 7 × 10-6 Katal. This value comes from converting the given rate of 420 μmoles per minute into the SI unit of katal (mol/s).
Step-by-Step Solution
Start with the given data: the enzyme converts 420 × 10-6 mol of substrate to product in 1 minute, or 60 seconds.
Divide by time to get the rate: (420 × 10-6 mol) / 60 s = 7 × 10-6 mol/s.
One katal equals 1 mol/s, so the activity is exactly 7 × 10-6 katal.
Options Analysis
- 1: Too low; assumes no unit conversion, ignoring μmol-to-mol and min-to-s factors.
- 3: Partial conversion error, e.g., forgetting to divide by 60 fully.
- 5: Common misstep from approximating 420/60 ≈ 7 but dropping a factor of 10-1.
- 7: Correct, as (420 × 10-6)/60 = 7 × 10-6 precisely.
Understanding Katal
The katal (kat) defines enzyme activity as moles of substrate converted per second. Unlike the international unit (IU, μmol/min), katal suits precise SI reporting but yields small numbers for typical lab rates. For enzyme activity katal conversion, always convert μmol to mol (×10-6) and minutes to seconds (/60).
Detailed Calculation
Given: 420 μmoles/min = 420 × 10-6 mol/60 s.
Rate = 420 × 10-6 / 60 = 7 × 10-6 mol/s = 7 × 10-6 katal.
This matches multiple-choice options where 7 is correct.
Common Pitfalls
- Forgetting μmol → mol: Yields 420/60 = 7, but in wrong units.
- Time error (min → s): Dividing by 1 instead of 60 gives 420 × 10-6.
- Use enzyme activity katal conversion formulas: activity (kat) = (μmoles/min × 10-6) / 60.
Practice Tips
- Memorize: 1 IU = 1 μmol/min ≈ 1.667 × 10-8 kat.
- For exams, verify steps: moles, time, then scale.
- Master enzyme activity katal conversion for NEET PG, MCAT, or biotech courses.
