Lowry Protein Assay: Principle, Protocol & Mechanism

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  • 0:00 Lowry Protein Assay Principle
  • 0:50 Steps in Reaction
  • 2:17 Mechanism of Reaction
  • 2:59 Lesson Summary
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Lesson Transcript
Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

The Lowry protein assay is a common method used to measure the protein concentration in products. In this lesson we will learn the steps in this method and how the reaction works.

Lowry Protein Assay Principle

When researchers investigate the effects of diseases or the health of an individual, the protein concentration of a patient's blood serum is often tested. Several different methods can be used to test the protein concentration. One of these is the Lowry protein assay, one of the most common methods used to measure the concentration of protein in a sample.

The Lowry protein assay uses copper, which bonds with the peptide bonds in proteins under alkaline conditions. This forms a monovalent copper ion which can then react with the Folin reagent, which in turn can be reduced into a blue colored substance. This blue color can be measured using a spectrophotometer to determine the concentration of blue in the sample. Thus, the concentration of protein can be determined.

Steps in Reaction

Let's go over the steps in the reaction. First a standard needs to be prepared. Oftentimes bovine serum albumin (BSA) is used as the standard. The standard and sample follow the sample steps for measuring the protein content. Since the protein content of the BSA is known, it can be used to convert the absorbance obtained from the sample to protein percentage in the sample.

Then the Lowry solution needs to be made. It consists of an alkaline solution, copper sulfate, and sodium tartrate. Then the Lowry solution can be mixed with the sample. This mixture needs to be incubated for 20 minutes to ensure that the reaction occurs. At this point the reaction is yellow. The Folins reagent is then added and, once again, the mixture is incubated.

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