Question

The concentration of a purified enzyme is 10 mg/mL. Ten microlitres of the enzyme solution in a total reaction volume of 1 mL catalyses the formation of 20 nanomoles of product in one minute under optimum conditions. The specific activity of the enzyme is .............. unit/mg. 
 

Hint:

Specific activity is the amount of product formed per minute per milligram of enzyme. Ensure to convert all units consistently (e.g., nanomoles to micromoles) for correct calculation.

Answer 1

Correct Answer: 0.2

Step 1: Calculate enzyme amount

$$\text{Enzyme amount} = 10 \text{ mg/mL} \times 0.01 \text{ mL} = 0.1 \text{ mg}$$

Step 2: Calculate enzyme activity

One unit of enzyme activity is defined as the amount of enzyme that catalyzes the conversion of 1 micromole of substrate per minute under optimum conditions.

Product formed per minute = 20 nanomoles = 0.02 micromoles

Step 3: Calculate specific activity

Specific activity is defined as enzyme units per mg of enzyme:

$$\text{Specific activity} = \frac{\text{Activity (units)}}{\text{Enzyme mass (mg)}}$$

$$= \frac{0.02 \text{ μmol/min}}{0.1 \text{ mg}}$$

$$= 0.2 \text{ units/mg}$$

Answer: 0.2 unit/mg