The key difference between bradford and lowry protein assay is that Bradford protein assay is based on the absorbance shift of the dye Coomassie brilliant blue G-250 while Lowry protein assay is based on the reaction of copper ions (Cu+) ions produced by the oxidation of peptide bonds with Folin–Ciocalteu reagent.
An assay is an analytical technique that helps to characterize the major functional components of a sample. Hence, an assay could be either a qualitative or quantitative test. Many fields including laboratory medicine, pharmacology, environmental biology, molecular biology, biochemistry, and immunology use this kind of assays routinely. Bradford and Lowry protein assay are two biochemical assays that determine the protein concentration in a sample solution. Both assays use colorimetric techniques to provide results.
CONTENTS
1. Overview and Key Difference
2. What is Bradford Protein Assay
3. What is Lowry Protein Assay
4. Similarities Between Bradford and Lowry Protein Assay
5. Side by Side Comparison – Bradford vs Lowry Protein Assay in Tabular Form
6. Summary
What is Bradford Protein Assay?
Bradford protein assay is a rapid spectroscopic analytical procedure for protein analysis. It shows high accuracy when measuring the protein concentration in a solution. Marion Bradford introduced this procedure in 1976. In this assay, the total reaction is based on the amino acid composition of the proteins measured. In other terms, Bradford protein assay is a colorimetric assay. It uses the dye Coomassie brilliant blue. Hence, this colorimetric protein assay depends on the absorbance shift of the dye. Coomassie brilliant blue G-250 exists in three formats: cationic (red), anionic (blue) and neutral (green). During acidic conditions, the red form of the dye gets converted to blue. It confirms the binding of the protein. If the protein is not present, the solution may remain in brown color.
Figure 01: Bradford protein assay
Bradford protein assay differs from other protein assays since it is less susceptible to interferences of various chemical compounds present in the protein solution. These compounds include sodium, potassium, glucose, and sucrose, etc.
What is Lowry Protein Assay?
Lowry protein assay is a biochemical assay used to determine the total level of protein in a solution. Oliver H. Lowry is the person who developed this reagent in 1940. The procedure depicts the total protein concentration of the solution by a color change that is proportional to the protein concentration in the solution. Hence, this is also a colorimetric protein assay.
The reaction between copper ions (Cu+) produced by the oxidation of peptide bonds and Folin–Ciocalteu reagent is the basis of this procedure. Also, this reagent contains phosphomolybdic acid and phosphor-tungstic acid. However, the reaction mechanism of Lowry protein assay is not well understood. But it involves the oxidation of cysteine, tryptophan and tyrosine residues by the reduction of Folin–Ciocalteu reagent.
Figure 02: Lowry protein assay
The cysteine residues contribute to the absorbance observed in Lowry protein assay and the reaction results in a brilliant blue molecule; heteropoly molybdenum blue. The reduction of this molecule is measured by absorbance at 660nm. Hence, the concentration of cysteine and tryptophan residues that reduced Folin–Ciocalteu reagent deduces the total concentration of the protein in the solution.
What are the Similarities Between Bradford and Lowry Protein Assay?
- Bradford and Lowry protein assays determine the protein concentration in a solution.
- Both methods are colourimetric methods.
- Also, the sensitivity of both methods is high.
What is the Difference Between Bradford and Lowry Protein Assay?
Bradford and Lowry protein assay are two types of assays that determine protein concentration in a solution. Bradford protein assay relies on the absorbance shift of the dye Coomassie brilliant blue G-250 while Lowry protein assay depends on the reaction of copper ions produced by the oxidation of peptide bonds, with Folin–Ciocalteu reagent. So, this is the key difference between Bradford and Lowry protein assay. Bradford protein assay takes 15 minutes to produce a result while Lowery protein assay takes 40-60 minutes to produce a result. Thus, this is another difference between Bradford and Lowry protein assay. Furthermore, Bradford protein assay is dependent on the amino acid composition while Lowry protein assay is partially dependent on the amino acid composition. Hence, this is also a difference between Bradford and Lowry protein assay.
Below inforaphic provides more details on the difference between Bradford and Lowry protein assay.
Summary – Bradford vs Lowry Protein Assay
An assay is an analytical technique used to characterize the major functional component of a sample. Bradford and Lowry protein assay are two types of protein assays that function under colorimetric techniques. Both Bradford and Lowry protein assays determine the protein concentration in a solution. However, the key difference between Bradford and Lowry Protein Assay lies on the colorimetric technique they use. Bradford protein assay uses the Coomassie brilliant blue G-250 while Lowry protein assay uses copper ions (Cu+) ions and Folin–Ciocalteu reagent. Furthermore, the Bradford method gives quick results than Lowry protein assay. However, both methods are highly sensitive methods and are subject to interferences from various substances.
Reference:
1. “Canadian Journal of Botany.” Canadian Journal of Botany – 60(7):1046 – PDF, Available here.
2. “Chemistry of Protein Assays.” Thermo Fisher Scientific – US, Available here.
Image Courtesy:
1. “Bradford protein assay” By Helito – Own work (CC BY-SA 4.0) via Commons Wikimedia