What is the Difference Between Specific Activity and Total Activity?

The difference between specific activity and total activity lies in their definitions and how they are used to measure the activity of proteins or radioisotopes. Here are the key differences:

• Specific Activity: Specific activity is the activity per quantity of a radionuclide or the enzymatic activity in the volume of fraction used in the assay divided by the total protein in the fraction. It serves as a measure of protein purity and can be used to determine whether a sample became purer following a purification step. Specific activity is typically expressed in units/mg or nmol/min/mg.
• Total Activity: Total activity is the total isotopic activity in the volume of the fraction used in the assay multiplied by the total volume of the sample. In the context of protein purification, total activity is the enzymatic activity in the volume of fraction used in the assay. Total activity is usually measured in units (u).

In summary, specific activity is a measure of protein purity and is calculated by dividing the total activity by the total protein, while total activity is the sum of all activity of the isotopes or enzymes in a given sample. Specifically, during protein purification, total activity represents the enzymatic activity in the volume of the fraction used in the assay, and specific activity is the ratio of that activity to the total protein.

Comparative Table: Specific Activity vs Total Activity

The difference between specific activity and total activity can be summarized as follows:

In the context of protein purification, specific activity is a measure of protein purity, calculated as enzyme units per milligram of protein. It helps to determine the purity of an enzyme preparation. On the other hand, total activity represents the sum of all activity in a sample, and it can be used to find the yield of a purification process.