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How to Calculate Specific Activities of Enzymes

By Chad Bjorklund

Enzymes are specialized proteins that serve as biocatalysts for nearly all the chemical reactions in a living organism. Without enzymes, the reactions that we would normally take for granted, like converting glucose into cellular energy, would never occur. Enzymatic activity is the rate at which an enzyme completes a chemical reaction and produces an end chemical product. The specific activity of an enzyme describes the enzymatic rate per milligram of enzyme.

Identify enzymatic reaction. Find data about the particular enzymatic reaction you are interested in; this is easily found online or in a textbook such as "Biochemistry,” written by Dr. Reginald Garret and Dr. Charles Grisham. As an example, look at the enzymatic reaction of alcohol dehydrogenase, an enzyme that converts an alcohol into an aldehyde.

Locate the enzymatic rate. The enzymatic rate is sometimes referred to as the enzyme unit. An EU is defined as the amount of product formed per minute under defined conditions, such as pH and temperature. In the example, alcohol dehydrogenase forms 30 micrograms of aldehyde per minute, at a pH 7.0 and a temperature of 37 degrees Celsius. Therefore, the EU of alcohol dehydrogenase is equal to 30 micrograms per minute.

Find the amount of enzyme. To determine specific activity, you will need to know the amount of enzyme required to produce a certain amount of product. The amount of product will need to be the same that is produced in a minute, which is used to determine the EU. In the example, 1 microgram of alcohol dehydrogenase was used to determine that the EU equals 30 micrograms per minute.

Calculate the specific activity. The specific activity of an enzyme is calculated by dividing the EU by the milligrams of enzyme used to calculate the EU. In the example with alcohol dehydrogenase, calculate the specific activity of this enzyme:

Specific activity = EU/milligrams of enzyme used

Specific activity of alcohol dehydrogenase = 30/1 = 30

Tips

Don’t get caught up in the details of the reaction. Many biochemical reactions facilitated by enzymes require multiple starting components and have multiple products. Only concentrate on the primary end product, since many of the other components are only necessary for the reaction to occur.

The example used here is not to be referenced as an absolute value and is only hypothetical. The specific activity of any particular enzyme can change, depending upon the conditions that the measurements or observations were made.

Warnings

If you use Internet-based information to find information for an enzymatic reaction, ensure that it is from a reliable source, such as a peer-reviewed scientific paper or from a university-based website.

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