Question

You are asked to measure the amount of β-glucosidase in a commercial enzyme solution containing 20 mg protein/mL of solution. You place 1 mL of this enzyme solution into 9 mL of an aqueous buffer solution containing 20 mM cellobiose. One unit of activity of β-glucosidase is defined as the amount of enzyme which produces 1 µmol of glucose per min in a 65 wt/v% solution of cellobiose at pH 5.0 and at 37°C. Initial rate experiments show that the reaction produces 1.8 µmol of glucose/mL.min. What is the specific activity of the commercial enzyme solution, in terms of # units/mg protein?

Answer 1

Unit of activity of β-glucosidase = amount enzyme / µmol of glucose per min

Unit of activity of β-glucosidase = 1mL of enzyme / 1.8 µmol of glucose per min

Unit of activity of β-glucosidase = 0.556 mL of enzyme/µmol of glucose per min = 0.556 units

Specific activity = 0.556 units / 20 mg protein

Specific activity = 0.0278 units / mg protein