Chymotrypsin has a molecular weight of approximately 25 000

Chymotrypsin has a molecular weight of approximately 25 000 g/mol. A stock solution of 0.25 mg of the enzyme was made in 10.0 mL of phosphate buffer at pH 7.8. A 100 microliter aliquot of this stock was diluted 50-fold. From this diluted solution, 50 microlitres was taken for assay in 1.0 mL of assay solution. The rate of production of product was 10.0 micromoles per minute. Based on the standard definition of international unit of an enzyme, determine the number of units of activity in the original solution of chymotrypsin.

Solution

An enzyme unit is defined as the enzyme activity that catalyses the conversion of 1 µmol substrate into product in one minute. By multiplying assay volume (in mL) with no. of product (in micromole) formed per minute, one can find the no. of units of enzyme.

Here the given assay volume is = 1.0 mL

substrate converted into the product per minute = 10 micromole

Hence the no. of enzyme units = 1.0 * 10 = 10 units