How to Judge the Quality of Proteinase K

by Katharine Martin

Often, enzymes such as proteinase K are evaluated heavily for their activity. Since the role of an enzyme is to hasten a chemical reaction, understanding enzymatic activity gives researchers a better idea of how well they will perform. The second component for evaluating the quality of proteinase K is looking at its purity. Contaminants such as RNase could dramatically reduce the efficiency of an experiment. In this article, we'll take a closer look at enzymatic activity and purity as ways of judging the quality of proteinase K.

Enzymatic Activity

Rather than its mass, an enzyme is evaluated for its activity and function. A way this is measured is in terms of enzyme units, which describes enzymatic activity. These units are expressed in international units (IU), and it refers to the amount of enzyme needed to convert 1 μmol of substrate to a given product in 1 minute.

An enzymatic reaction occurs in three steps:

The enzyme and substrate are mixed together
The substrate binds to the enzyme’s active site forming an enzyme-substrate complex
The reaction occurs forming a product dissociated from the enzyme.

Enzymatic activity illustration, understanding how enzymatic activity works, proteinase K activity, judging the quality of enzymes and proteinase K

Therefore, activity looks at an enzyme’s ability to speed up the reaction rate, which is one of the most important characteristics in judging an enzyme.

Higher enzymatic activity in your reagent means you need less of that reagent. The same goes with proteinase K. The more active it is, the less you use.

There are more considerations for activity to keep in mind when using proteinase K. For more information about how activity impacts protocol use, take a look at our article “The Ultimate guide to Proteinase Activity & Concentration (u/mL).”

Proteinase K Purity

Proteinase K is a protease, which is often used during DNA and RNA isolation. During DNA isolation, proteinase K protects DNA from destructive nucleases. It also degrades proteins in DNA and RNA mixtures, for example a protein capsid, which helps with the extraction process.

Because of its broad-spectrum nature, proteinase K digests contaminating proteins and nucleases.

Therefore, the purity of proteinase K is important because it impacts its enzymatic activity. Using a proteinase K that is free of DNases and RNases ensures your DNA extraction will yield greater results. Proteinase K specifically tested and cleared of any RNase activity is ideal for your extraction. Be sure to read over your vendor’s certificate of analysis to determine the purity of proteinase K.