Why is specific activity used as a measurement of enzyme purity, but the turnover number cannot be used for this purpose?

See explanation

Explanation:

Specific activity of an enzyme is defined as a measure of the rate of reaction between enzyme and substrate.

In the study of enzyme kinetics, specific activity is particularly regarded to be the amount of substrate converted by the enzyme per milligram of protein per unit of time. It is thus a reliable measure of enzyme activity per milligram of total protein.

On the other hand, the turnover number is defined as a measure of the number of conversions achieved by a substrate molecule in one second at a particular active site depending on the specific enzyme concentration.

Since specific activityof the enzyme is the ratio of the enzyme activity to enzyme concentration, then specific activity can be used as a measurement of enzyme purity.